Author name code: donea
ADS astronomy entries on 2022-09-14
author:"Donea, Alina C."
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Title: Thermal and Non-thermal Properties of Active Region Recurrent
Coronal Jets
Authors: Paraschiv, Alin R.; Donea, Alina C.; Judge, Philip G.
Bibcode: 2022ApJ...935..172P
Altcode: 2022arXiv220712612P
We present observations of recurrent active region coronal jets,
and derive their thermal and non-thermal properties, by studying
the physical properties of the plasma simultaneously at the base
footpoint and along the outflow of jets. The sample of analyzed solar
jets were observed by SDO-AIA in extreme ultraviolet and by RHESSI
in the X-ray domain. The main thermal plasma physical parameters,
such as temperature, density, energy flux contributions, etc.,
are calculated using multiple inversion techniques to obtain the
differential emission measure from extreme-ultraviolet filtergrams. The
underlying models are assessed, and their limitations and applicability
are scrutinized. Complementarily, we perform source reconstruction
and spectral analysis of higher energy X-ray observations to further
assess the thermal structure and identify non-thermal plasma emission
properties. We discuss a peculiar penumbral magnetic reconnection
site, which we previously identified as a "Coronal Geyser." Evidence
supporting cool and hot thermal emission, as well as non-thermal
emission, is presented for a subset of geyser jets. These active
region jets are found to be energetically stronger than their polar
counterparts, but we find their potential influence on heliospheric
energetics and dynamics to be limited. We scrutinize whether the
geyser does fit the non-thermal erupting microflare picture, finding
that our observations at peak flaring times can only be explained by a
combination of thermal and non-thermal emission models. This analysis
of geysers provides new information and observational constraints
applicable to theoretical modeling of solar jets.
Title: Thank You to Our 2021 Reviewers
Authors: Caprarelli, Graziella; Altintas, Ilkay; Baratoux, David;
Cervato, Cinzia; Diviacco, Paolo; Donea, Alina; Donnellan, Andrea;
Gentemann, Chelle; Glaves, Helen M.; Jiang, Jonathan H.; Jones,
Cathleen E.; Maute, Astrid; Pirenne, Benoit; Pryor, Sara C.; Tiampo,
Kristy; Xie, Zunyi
Bibcode: 2022E&SS....902372C
Altcode:
On behalf of the Editorial Board and Staff of Earth and Space Science,
I thank the reviewers whose selfless dedication to science has ensured,
once again, that the papers published in our journal in 2021 highlight
the best Earth and space science in a manner that does justice to the
authors and their work. All of us at Earth Peer reviewing is a demanding
and often thankless job. It is however an essential component of the
scientific process, ensuring the highest standards of integrity and
rigor. Without the work of reviewers, who check data and procedures
for possible bias and to ensure reproducibility, and who share their
expertise to verify that the interpretations and conclusions of a
paper are consistent with assumptions and existing knowledge, it would
not be possible to trust in the scientific process. Our journal is
particularly indebted to our reviewers: Earth and Space Science is a
multidisciplinary journal that highlights methods, instruments, data
and algorithms, and therefore we rely heavily on the direct expertise
of our reviewers to verify and vouch for the quality of the papers we
publish. We are indebted to all our reviewers, and we are delighted
to acknowledge them publicly in this Editorial.
Title: Second bounces of seismic signals from sunquakes: modelling
and data
Authors: Donea, A.; Cally, P.
Bibcode: 2021AAS...23811318D
Altcode:
The 6 September 2017 X9.3 solar flare produced interesting magnetic
field transients and a few seismic sources generating visible acoustic
ripples in the quiet magnetic bay of the hosting active region.Zharkov
et al (2020) for the first time presented observations of the second
bounce of acoustic waves generated in the solar photosphere by one of
the seismic sources. In this work we model the second skips using the
ray-theory and simple models of magnetic fields of a sunspot. We want
to understand how various parametrisations related to the local magnetic
field, source locations and source movements can influence the behaviour
of the first and second skips in time-distance plots. This work will
help us to understand why the majority of sunquakes do not present
second bounces; it may give us clues on how to look at observations
in search for ripples and will help with backtracking information on
seismic sources.
Title: What on Sun can be so fast at that depth to trigger such a
deeply emerged seismic source?
Authors: Donea, Alina; Charlie, Lindsey; Martinez Oliveros, Juan Carlos
Bibcode: 2021cosp...43E1781D
Altcode:
Flares can create seismic activity — sunquakes — releasing impulsive
acoustic waves that penetrate deep into the sun's interior. Recent
findings (Lindsey et al, 2020) suggest that these "acoustic transients"
— and the sunquakes they generate — can reveal a lot about flares
and can help with the diagnostic whether the size and severity of a
flare may be relevant for driving significant solar eruptions. Here
we report that an unusual seismic source, part of the acoustic
energy released from the July 30, flare in 2011, emanated from about
1,000 kilometers beneath the solar surface. This flare was extremely
impulsive. This location is deep into the Sun, far beneath the solar
flare that triggered the seismic event. The helioseismic holography
method revealed the location and the strength of the seismic source. In
this work we will present the properties of this solarquake, its
unique source and address the issue related to whether the submerged
acoustic source is a spoiler of a bigger event, that might lead us to
a forecasting tool. We acknowledge the team work of all the authors
of the paper (Lindsey et al, 2020) who contributed to the discovery
of the submerged event.
Title: Training magnetic and seismic data sets for machine learning
algorithms to detect magnetic polarities of far side solar regions
Authors: Donea, Alina; Smith, Cameron
Bibcode: 2021cosp...43E1786D
Altcode:
The training data set in machine learning is gaining mainstream
presence for data and solar scientists nowdays via its implementation
of a series of algorithms for the autonomous detection and tracking of
solar features in the Sun's far hemisphere. Lindsey & Braun (2000)
introduced the concept of far-side imaging, in which observations
of the solar oscillations made on the visible disk are used to infer
the presence of active regions on the far-side of the Sun. Using the
far-side seismic monitor, large active regions in the far hemisphere can
be detected. This is well established. To identify the magnetic polarity
of this region we aim to build an accurate machine learning GaNc-based
predictive model to image the solar magnetic polarity. Statistics
data based on the complexity and the accuracy of the estimates of
magnetic structure and seismicity on the far side will be presented,
and compared to the near side. In this paper, we will also present
the training data set and ask incipient questions about what is the
sensitivity in the train model to influence the estimates of the
magnetic polarities of solar regions or near and far side of the Sun.
Title: Spectral Contrast in Chromospheric Quiescent Emission
Authors: Lacatus, D.; Donea, A. C.
Bibcode: 2020AGUFMSH0010004L
Altcode:
Quiescent conditions are not easily distinguishable from each other in
integrated chromospheric emission, especially when they are underlying
different coronal structures or are neighboring different large scale
magnetic configurations. In this study we are using datasets from
the Interface Region Imaging Spectrograph (IRIS) to investigate the
statistical properties of such 'quiet' emission in order to identify
those observables that can be used to differentiate such regions. We
developed and employed a fast profile features identification algorithm
for the Mg II resonance lines emission, to probe the chromospheric
contrast based on different Mg II spectral features. The correlation
between these spectroscopic measurements is discussed in the context of
their relation to each other and to the emitting plasma. Overall, the
Inter-network regime is dominated by signatures of convective motions,
which become suppressed in the Network, where the magnetic field leads
to increased emission. We found that the line width and peak separation
are enhanced under coronal holes compared to the other conditions
considered, while the other measurement are only marginally sensitive.
Title: On Recurrent Active Region Coronal Jets: Coronal Geyser
Sources of Electron Beams and Interplanetary Type-III Radio Bursts
Authors: Paraschiv, A.; Donea, A. C.
Bibcode: 2020AGUFMSH0240007P
Altcode:
No abstract at ADS
Title: Observations of the 86 GHz SiO maser sources in the Central
Parsec of the Galactic Centre
Authors: Borkar, A.; Eckart, A.; Straubmeier, C.; Sabha, N.;
Sjouwerman, L. O.; Karas, V.; Kunneriath, D.; Moser, L.; Britzen,
S.; Valencia-Schneider, M.; Donea, A.; Zensus, A.
Bibcode: 2020mbhe.confE..33B
Altcode: 2020PoS...362E..33B; 2019mbhe.confE..33B; 2019arXiv190913753B
We present results of 3 mm observations of SiO maser sources in the
Galactic Centre (GC) from observations with the Australia Telescope
Compact Array between $2010-2014$, along the transitions of the SiO
molecule at $v = 1, J = 2-1$ at 86.243 GHz and $v = 2, J = 2-1$ at
85.640 GHz. We also present the results of the 3 mm observations with
Atacama Large Millimeter/Submillimeter Array (ALMA). We detected 5 maser
sources from the ATCA data, IRS 7, IRS 9, IRS 10EE, IRS 12N, and IRS 28;
and 20 sources from the ALMA data including 4 new sources. These sources
are predominantly late-type giants or emission line stars with strong
circumstellar maser emission. We analyse these sources and calculate
their proper motions. We also study the variability of the maser
emission. IRS 7, IRS 12N and IRS 28 exhibit long period variability of
the order of $1 - 2$ years, while other sources show steady increase
or decrease in flux density and irregular variability over observation
timescales. This behaviour is consistent with the previous observations.
Title: Submerged Sources of Transient Acoustic Emission from Solar
Flares
Authors: Lindsey, Charles; Buitrago-Casas, J. C.; Martínez Oliveros,
Juan Carlos; Braun, Douglas; Martínez, Angel D.; Quintero Ortega,
Valeria; Calvo-Mozo, Benjamín; Donea, Alina-Catalina
Bibcode: 2020ApJ...901L...9L
Altcode:
We report the discovery of ultra-impulsive acoustic emission from
a solar flare, emission with a seismic signature that indicates
submersion of its source approximately a Mm beneath the photosphere
of the active region that hosted the flare. Just over two decades ago
V. V. Zharkova and A. G. Kosovichev discovered the first acoustic
transient released into the Sun's interior by a solar flare. These
acoustic waves, refracted back upward to the solar surface after
their release, make conspicuous Doppler ripples spreading outward
from the flaring region that tell us a lot about their sources. The
mechanism by which these transients are driven has stubbornly eluded
our understanding. Some of the source regions, for example, are devoid
of secondary Doppler, magnetic, or thermal disturbances in the outer
atmosphere of the source regions that would signify the driving agent
of an intense seismic transient in the outer atmosphere. In this
study, we have applied helioseismic holography, a diagnostic based
upon standard wave optics, to reconstruct a 3D image of the sources
of acoustic waves emanating from the M9.3-class flare of 2011 July
30. These images contain a source component that is submerged a full
Mm beneath the active-region photosphere. The signature of acoustic
sources this deep in the solar interior opens new considerations into
the physics that must be involved in transient acoustic emission from
flares—and possibly of flare physics at large. We develop analogies
to seismicity remotely triggered by tremors from distant earthquakes,
and consider prospects of new insight into the architecture of magnetic
flux beneath flaring active regions.
Title: Quiet Sun Emission in the Mg II Resonance Lines
Authors: Lacatus, D. A.; Donea, A.
Bibcode: 2020SPD....5120103L
Altcode:
We present a comprehensive investigation of the Mg II k&h
lines profiles under quiet solar conditions, as seen by IRIS. An in
depth analysis of the various profile characteristics is provided,
considering datasets covering diverse surrounding large scale magnetic
configurations and different local activity levels, from pure quiet
sun to regions underlying coronal holes or located under the active
region canopy. The line profile characteristics are identified, the
differences between Network and Inter-network regimes are characterized
and the evolution of similar activity conditions is discussed. The
statistical properties of the different activity levels are explored
and the correlations between the different computed parameters are
evaluated. Overall, the Inter-network regime is dominated by signatures
of convective motions, which become suppressed in the Network, where
the magnetic field leads to enhanced emission.
Title: The Trigger Mechanism of Recurrent Solar Active Region Jets
Revealed by the Magnetic Properties of a Coronal Geyser Site
Authors: Paraschiv, Alin Razvan; Donea, Alina; Leka, K. D.
Bibcode: 2020ApJ...891..149P
Altcode: 2020arXiv200211819P
Solar active region jets are small-scale collimated plasma eruptions
that are triggered from magnetic sites embedded in sunspot penumbral
regions. Multiple trigger mechanisms for recurrent jets are under
debate. Vector magnetic field data from Solar Dynamics Observatory
(SDO) Helioseismic and Magnetic Imager (HMI) observations are used to
analyze a prolific photospheric configuration, identified in extreme
ultraviolet observations as a "coronal geyser," that triggered a set of
at least 10 recurrent solar active region jets. We focus on interpreting
the magnetic fields of small-scale flaring sites aiming to understand
the processes that govern recurrent jet eruptions. We perform a custom
reprocessing of the SDO-HMI products, including disambiguation and
uncertainty estimation. We scrutinized the configuration and dynamics
of the photospheric magnetic structures. The magnetic configuration
is described, via the analysis of the photospheric magnetic vertical
fields, to identify the process that is responsible for driving
the jet eruptions. We report that the two widely debated magnetic
trigger processes, namely magnetic flux cancellation and magnetic
flux emergence, appear to be responsible on a case by case basis for
generating each eruption in our set. We find that 4 out of 10 jets
were due to flux cancellation, while the rest were clearly not and
were more likely due to flux emergence.
Title: On Solar Recurrent Coronal Jets: Coronal Geysers as Sources
of Electron Beams and Interplanetary Type-III Radio Bursts
Authors: Paraschiv, Alin Razvan; Donea, Alina
Bibcode: 2019ApJ...873..110P
Altcode: 2019ApJ...873..110R; 2019arXiv190304682R
Coronal jets are transitory small-scale eruptions that are omnipresent
in solar observations. Active regions jets produce significant
perturbations on the ambient solar atmosphere and are believed to be
generated by microflare reconnection. Multiple sets of recurrent jets
are identified in extreme-ultraviolet filter imaging. In this work
we analyze the long timescale recurrence of coronal jets originating
from a unique footpoint structure observed in the lower corona. We
report the detection of penumbral magnetic structures in the lower
corona. These structures, which we call “coronal geysers,”
persist through multiple reconnection events that trigger recurrent
jets in a quasi-periodical trend. Recurrent jet eruptions have been
associated with Type-III radio bursts that are manifestations of
traveling non-thermal electron beams. We examine the assumed link, as
the coronal sources of interplanetary Type-III bursts are still open
for debate. We scrutinized the hypothesized association by temporally
correlating a statistically significant sample of six Geyser structures
that released at least 50 recurrent jets, with correspondent Type-III
radio bursts detected in the interplanetary medium. Data analysis of
these phenomena provides new information on small-scale reconnection,
non-thermal electron beam acceleration, and energy release. We find
that the penumbral Geyser-like flaring structures produce recurring
jets. They can be long-lived, quasi-stable, and act as coronal sources
for Type-III bursts, and, implicitly, upward accelerated electron beams.
Title: Low Altitude Solar Magnetic Reconnection, Type III Solar
Radio Bursts, and X-ray Emissions
Authors: Cairns, I. H.; Lobzin, V. V.; Donea, A.; Tingay,
S. J.; McCauley, P. I.; Oberoi, D.; Duffin, R. T.; Reiner, M. J.;
Hurley-Walker, N.; Kudryavtseva, N. A.; Melrose, D. B.; Harding, J. C.;
Bernardi, G.; Bowman, J. D.; Cappallo, R. J.; Corey, B. E.; Deshpande,
A.; Emrich, D.; Goeke, R.; Hazelton, B. J.; Johnston-Hollitt, M.;
Kaplan, D. L.; Kasper, J. C.; Kratzenberg, E.; Lonsdale, C. J.; Lynch,
M. J.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan,
E.; Ord, S. M.; Prabu, T.; Roshi, A.; Shankar, N. Udaya; Srivani,
K. S.; Subrahmanyan, R.; Wayth, R. B.; Waterson, M.; Webster, R. L.;
Whitney, A. R.; Williams, A.; Williams, C. L.
Bibcode: 2018NatSR...8.1676C
Altcode:
Type III solar radio bursts are the Sun's most intense and frequent
nonthermal radio emissions. They involve two critical problems in
astrophysics, plasma physics, and space physics: how collective
processes produce nonthermal radiation and how magnetic reconnection
occurs and changes magnetic energy into kinetic energy. Here magnetic
reconnection events are identified definitively in Solar Dynamics
Observatory UV-EUV data, with strong upward and downward pairs of
jets, current sheets, and cusp-like geometries on top of time-varying
magnetic loops, and strong outflows along pairs of open magnetic field
lines. Type III bursts imaged by the Murchison Widefield Array and
detected by the Learmonth radiospectrograph and STEREO B spacecraft
are demonstrated to be in very good temporal and spatial coincidence
with specific reconnection events and with bursts of X-rays detected
by the RHESSI spacecraft. The reconnection sites are low, near heights
of 5-10 Mm. These images and event timings provide the long-desired
direct evidence that semi-relativistic electrons energized in magnetic
reconnection regions produce type III radio bursts. Not all the observed
reconnection events produce X-ray events or coronal or interplanetary
type III bursts; thus different special conditions exist for electrons
leaving reconnection regions to produce observable radio, EUV, UV,
and X-ray bursts.
Title: What can He II 304 Å tell us about transient seismic emission
from solar flares?
Authors: Lindsey, C.; Donea, A. C.
Bibcode: 2017IAUS..327..113L
Altcode:
After neary 20 years since their discovery by Kosovichev and Zharkova,
the mechanics of the release of seismic transients into the solar
interior from some flares remain a mystery. Seismically emissive
flares invariably show the signatures of intense chromosphere
heating consistent with pressure variations sufficient to drive
seismic transients commensurate with helioseismic observations-under
certain conditions. Magnetic observations show the signatures of
apparent magnetic changes, suggesting Lorentz-force transients that
could likewise drive seismic transients-similarly subject to certain
conditions. But, the diagnostic signatures of both of these prospective
drivers are apparent over vast regions from which no significant
seismic emission emanates. What distinguishes the source regions of
transient seismic emission from the much vaster regions that show the
signatures of both transient heating and magnetic variations but are
acoustically unproductive? Observations of acoustically active flares
in He II 304 Å by the Atomospheric Imaging Assembly (AIA) aboard the
Solar Dynamics Observatory (SDO) offer a promising new resource with
which to address this question.
Title: An Explanation of Remarkable Emission-line Profiles in
Post-flare Coronal Rain
Authors: Lacatus, Daniela A.; Judge, Philip G.; Donea, Alina
Bibcode: 2017ApJ...842...15L
Altcode: 2017arXiv170707069L
We study broad redshifted emission in chromospheric and transition
region lines that appears to correspond to a form of post-flare
coronal rain. Profiles of Mg II, C II, and Si IV lines were obtained
using IRIS before, during, and after the X2.1 flare of 2015 March 11
(SOL2015-03-11T16:22). We analyze the profiles of the five transitions
of Mg II (the 3p-3s h and k transitions, and three lines belonging to
the 3d-3p transitions). We use analytical methods to understand the
unusual profiles, together with higher-resolution observational data
of similar phenomena observed by Jing et al. The peculiar line ratios
indicate anisotropic emission from the strands that have cross-strand
line center optical depths (k line) of between 1 and 10. The lines
are broadened by unresolved Alfvénic motions whose energy exceeds
the radiation losses in the Mg II lines by an order of magnitude. The
decay of the line widths is accompanied by a decay in the brightness,
suggesting a causal connection. If the plasma is ≲99% ionized,
ion-neutral collisions can account for the dissipation; otherwise, a
dynamical process seems necessary. Our work implies that the motions are
initiated during the impulsive phase, to be dissipated as radiation over
a period of an hour, predominantly by strong chromospheric lines. The
coronal “rain” we observe is far more turbulent than most earlier
reports have indicated, with implications for plasma heating mechanisms.
Title: Are All Flare Ribbons Simply Connected to the Corona?
Authors: Judge, Philip G.; Paraschiv, Alin; Lacatus, Daniela; Donea,
Alina; Lindsey, Charlie
Bibcode: 2017ApJ...838..138J
Altcode: 2017arXiv170707072J
We consider the observational basis for the belief that flare
ribbons in the chromosphere result from energy transport from the
overlying corona. We study ribbons of small flares using magnetic
and intensity data from the Hinode, Solar Dynamics Observatory, and
IRIS missions. While most ribbons appear connected to the corona and
overlie regions of significant vertical magnetic field, we examine
one ribbon with no clear evidence for such connections. Evolving
horizontal magnetic fields seen with Hinode suggest that reconnection
with preexisting fields below the corona can explain the data. The
identification of just one, albeit small, ribbon, with no apparent
connection to the corona, leads us to conclude that at least two
mechanisms are responsible for the heating that leads to flare ribbon
emission. The National Center for Atmospheric Research is sponsored
by the National Science Foundation.
Title: Current State of Seismic Emission Associated with Solar Flares
Authors: Besliu-Ionescu, D.; Donea, A.; Cally, P.
Bibcode: 2017SunGe..12...59B
Altcode:
Certain solar flares are followed by photospheric seismic emission,
also known as sunquakes. Sunquakes were predicted more than 40 years
ago, but observed for the first time 20 years ago. A valid scenario
that would fit all discoveries made so far is still missing. This paper
summarises the current state of the literature concerning sunquakes. It
describes all published reports of known seismic sources to date and
presents possible triggering mechanisms.
Title: MWA Observations of Solar Radio Bursts and the Quiet Sun
Authors: Cairns, I.; Oberoi, D.; Morgan, J.; Bastian, T.; Bhatnagar,
S.; Bisi, M.; Benkevitch, L.; Bowman, J.; Donea, A.; Giersch, O.;
Jackson, B.; Chat, G. L.; Golub, L.; Hariharan, K.; Herne, D.; Kasper,
J.; Kennewell, J.; Lonsdale, C.; Lobzin, V.; Matthews, L.; Mohan, A.;
Padmanabhan, J.; Pankratius, V.; Pick, M.; Subramanian, P.; Ramesh,
R.; Raymond, J.; Reeves, K.; Rogers, A.; Sharma, R.; Tingay, S.;
Tremblay, S.; Tripathi, D.; Webb, D.; White, S.; Abidin, Z. B. Z.
Bibcode: 2017mwa..prop..A06C
Altcode:
A hundred hours of observing time for solar observations is requested
during the 2017-A observing semester. These data will be used to address
science objectives for solar burst science (Goal A), studies of weak
non-thermal radiation (Goal B) and quiet sun science (Goal C). Goal
A will focus on detailed investigations of individual events seen in
the MWA data, using the unsurpassed spectroscopic imaging ability
of the MWA to address some key solar physics questions. Detailed
observations of type II bursts, of which MWA has observed two, will
be one focus, with MWA polarimetric imaging observations of type III
bursts another focus. Goal B will address studies of the numerous
short lived and narrow band emission features, significantly weaker
than those seen by most other instruments revealed by the MWA. These
emission features do not resemble any known types of solar bursts, but
are possible signatures of "nanoflares" which have long been suspected
to play a role in coronal heating. A large database of these events is
needed to be able to reliably estimate their contribution to coronal
heating. These observations will contribute to this database. Goal C
will focus on characterizing the Sun's background thermal emission,
their short and long term variability and looking for evidence of a
scattering disc around the Sun.
Title: On Recurrent/Homologous Coronal Jets Emission: Coronal Geyser
Structures
Authors: Paraschiv, Alin Razvan; Donea, Alina
Bibcode: 2016shin.confE.115P
Altcode:
Active region 11302 has shown a vast display of solar jets during its
lifetime. We examine the emission mechanism responsible for multiple
coronal jet events occurring at the center-east side of the active
region. Identified jet events were detected in extreme-ultraviolet
(EUV), hard X-ray (HXR) and radio emissions, observed by dedicated
instruments such as SDO's AIA and HMI, STEREO's EUVI and WAVES, and
RHESSI, respectively. We report the detection of a base-arch structure
in the lower atmosphere. The site was labelled
Title: The March 11, 2015 X2.1 flare: peculiar post-flare spectral
signatures
Authors: Lacatus, Daniela Adriana; Donea, A.; Judge, P. G.
Bibcode: 2016shin.confE.207L
Altcode:
The only X-class flare of 2015 observed by IRIS occurred at 16:22
UT on 11 March 2015, in AR 12297. This flare generated significant
seismic transients in the photosphere at the eastern location of the
flare. IRIS observations of the chromosphere and transition region
help us understand the physics of the sunquake. In this work we will
analyze this event using data from IRIS, SDO, and RHESSI. Unfortunately,
the IRIS rasters scanned the area between the main footpoints of the
solar flare. Whereas, the main X-ray emission dominates the eastern
footprint. Significant enhancements in the chromospheric and TR lines
intensities were measured. The forbidden line of Fe XXI 1354.1 Å
is detected after the flare peak. Important plasma downflows were
identified in the majority of the observed lines, consistent with
magnetic field reconfiguration. An erupting filament develops at 16:12
UT and moves rapidly towards the eastern part of the active region.
Title: Monitoring the Galactic Centre with the Australia Telescope
Compact Array
Authors: Borkar, A.; Eckart, A.; Straubmeier, C.; Kunneriath,
D.; Jalali, B.; Sabha, N.; Shahzamanian, B.; García-Marín, M.;
Valencia-S, M.; Sjouwerman, L.; Britzen, S.; Karas, V.; Dovčiak,
M.; Donea, A.; Zensus, A.
Bibcode: 2016MNRAS.458.2336B
Altcode: 2016arXiv160500424B; 2016MNRAS.tmp..147B
The supermassive black hole, Sagittarius A* (Sgr A*), at the
centre of the Milky Way undergoes regular flaring activity, which
is thought to arise from the innermost region of the accretion
flow. Between 2010 and 2014, we performed monitoring observations
of the Galactic Centre to study the flux-density variations at 3 mm
using the Australia Telescope Compact Array (ATCA). We obtain light
curves of Sgr A* by subtracting the contributions from the extended
emission around it, and the elevation and time-dependent gains of the
telescope. We perform structure function analysis and the Bayesian
blocks representation to detect flare events. The observations detect
six instances of significant variability in the flux density of Sgr A*
in three observations, with variations between 0.5 and 1.0 Jy, which
last for 1.5-3 h. We use the adiabatically expanding plasmon model to
explain the short time-scale variations in the flux density. We derive
the physical quantities of the modelled flare emission, such as the
source expansion speed vexp, source sizes, spectral indices
and the turnover frequency. These parameters imply that the expanding
source components are either confined to the immediate vicinity of Sgr
A* by contributing to the corona or the disc, or have a bulk motion
greater than vexp. No exceptional flux-density variation
on short flare time-scales was observed during the approach and the
flyby of the dusty S-cluster object (DSO/G2). This is consistent with
its compactness and the absence of a large bow shock.
Title: Spectral response of the solar atmosphere to an X-class
flare event
Authors: Lacatus, Daniela Adriana; Donea, Alina
Bibcode: 2016SPD....4740306L
Altcode:
The only X-class flare of 2015 observed by IRIS occurred at 16:22
UT on 11 March 2015, in AR 12297. This flare generated significant
seismic transients in the photosphere at the eastern location of the
flare. IRIS observations of the chromosphere and transition region
help us understand the physics of the sunquake. In this work we will
analyse this event using data from IRIS, SDO, and RHESSI. The IRIS
rasters scanned the area between the main footpoints of the solar flare,
and a wealth of chromospheric information has been inferred about the
dynamics of the event. The main X-ray emission dominates the eastern
flare footpoint, being missed by the IRIS slit. Significant enhancements
in the chromospheric and TR lines intensities were identified. The
forbidden line of Fe XXI 1354.1 Å is detected after the flare peak
revealing the coronal responses to the flare. Plasma downflows of up
to 300 km/s were identified in the majority of the observed lines,
consistent with magnetic field local reconfiguration. We have also
analysed an erupting filament developing at an earlier time, which
moved rapidly towards the eastern part of the active region. We discuss
the possibility that this filament might have pre-conditioned the
chromosphere for the flare process.
Title: Seismic Ripple Anisotropy on the photosphere: observed,
simulated, explained
Authors: Donea, Alina
Bibcode: 2016SPD....4720306D
Altcode:
Based on observations of seismic ripples generated by solar flares,
we performed simulations of different configurations/ morphologies of
acoustic structures at the "epicenter" of the sunquake, The production
of seismic waves is caused by spatially confined, high impacts into
the solar photosphere, inflicted during the impulsive phase of solar
flares.An interesting characteristic feature of the seismic response of
most sunquakes is a considerable anisotropy in acoustic amplitude of the
ripples from the vantage of the source, the acoustic emission is much
stronger in some directions than others.We have produced a catalogue
of simulations showing varying degrees of wave front anisotropy. Due
to the large number of parameters that have potential for variation
within the code, an innumerable number of cases have the capacity to
be constructed. The governing limits of variation for each parameter
will therefore be restricted to those of real life physical situations
that have either been observed or strongly proposed. I will present
the most conclusive cases of our work, which elucidate some of the
unsolved clues about sunquakes and their ripples.
Title: On Recurrent/Homologous Coronal Jets Emission: Coronal Geyser
Structures
Authors: Paraschiv, Alin Razvan; Donea, Alina
Bibcode: 2016SPD....47.0325P
Altcode: 2016SPD....47.0325R
Active region 11302 has shown a vast display of solar jets during its
lifetime. We examine the emission mechanism responsible for multiple
coronal jet events occurring at the center-east side of the active
region. Identified jet events were detected in extreme-ultraviolet
(EUV), hard X-ray (HXR) and radio emissions, observed by dedicated
instruments such as SDO's AIA and HMI, STEREO's EUVI and WAVES, and
RHESSI, respectively. We report the detection of a base-arch structure
in the lower atmosphere. The site was labelled "Coronal Geyser". The
structure had emitted jets quasi-periodically for the entire time
the AR was visible in SDO'S field of view. The jets expand into the
corona with an apparent line of sight velocity of ~200-300$ km/s. To
our knowledge the long time-scale behaviour of jet recurrence and base
geyser structure was not previously discussed and data analysis of
this phenomena will provide new information for theoretical modelling
and data interpretation of jets.
Title: On mode conversion, reflection, and transmission of
magnetoacoustic waves from above in an isothermal stratified
atmosphere
Authors: Hansen, Shelley C.; Cally, Paul S.; Donea, Alina-C.
Bibcode: 2016MNRAS.456.1826H
Altcode: 2015arXiv151107364H
We use the exact solutions for magnetoacoustic waves in a
two-dimensional (2D) isothermal atmosphere with uniform inclined
magnetic field to calculate the wave reflection, transmission, and
conversion of slow and fast waves incident from above (z = ∞). This is
relevant to the question of whether waves excited by flares in the solar
atmosphere can penetrate the Alfvén/acoustic equipartition layer (which
we identify as the canopy) to reach the photosphere with sufficient
energy to create sunquakes. It is found that slow waves above the
acoustic cutoff frequency efficiently penetrate (transmit) as acoustic
(fast) waves if directed at a small attack angle to the magnetic field,
with the rest converting to magnetic (slow) waves, in accord with
Generalized Ray Theory. This may help explain the compact nature of
seismic sources of sunquakes identified using seismic holography. The
incident slow waves can also efficiently transmit at low frequency
in inclined field due to the reduction in acoustic cutoff frequency
(ramp effect). Incident fast (magnetic) `waves' from infinity with
specified non-zero horizontal wavenumber are necessarily evanescent,
but can carry energy to the equipartition level by tunnelling. It is
found that this can then efficiently convert to acoustic (fast) energy
that can again reach the photosphere as a travelling wave. Overall,
there appear to be ample avenues for substantial compressive wave
energy to penetrate the canopy and impact the photosphere.
Title: Solar chromosphere: a portal for sunquakes
Authors: Donea, A. C.; Lindsey, C. A.
Bibcode: 2015AGUFMSH22A..02D
Altcode:
Recent solar images from instruments such as IRIS, FIRS, IBIS and SDO
reveal interesting properties of the chromosphere and other layers
above flaring active regions . These may finally give us some clues on
why some solar flares allow an energy input back into the photosphere,
generating sunquakes. We will discuss recent observations of sunquakes
and analyse the main role of the "right chromosphere" for a sunquake
event.
Title: Enhanced Acoustic Emission in Relation to the Acoustic Halo
Surrounding Active Region 11429
Authors: Hanson, Chris S.; Donea, Alina C.; Leka, K. D.
Bibcode: 2015SoPh..290.2171H
Altcode: 2015arXiv150703447H; 2015SoPh..tmp...93H
The use of acoustic holography in the high-frequency p -mode spectrum
can resolve the source distributions of enhanced acoustic emissions
within halo structures surrounding active regions. In doing so,
statistical methods can then be applied to ascertain relationships with
the magnetic field. This is the focus of this study. The mechanism
responsible for the detected enhancement of acoustic sources around
solar active regions has not yet been explained. Furthermore the
relationship between the magnetic field and enhanced acoustic
emission has not yet been comprehensively examined. We have used
vector magnetograms from the Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory (SDO) to image the magnetic-field
properties in the halo. We have studied the acoustic morphology of an
active region, with a complex halo and "glories", and we have linked
some acoustic properties to the magnetic-field configuration. In
particular, we find that acoustic sources are significantly enhanced in
regions of intermediate field strength with inclinations no different
from the distributions found in the quiet Sun. Additionally, we have
identified a transition region between the active region and the halo,
in which the acoustic-source power is hindered by inclined fields of
intermediate field strength. Finally, we have compared the results of
acoustic-emission maps, calculated from holography, and the commonly
used local acoustic maps, finding that the two types of maps have
similar properties with respect to the magnetic field but lack spatial
correlation when examining the highest-powered regions.
Title: On the Origin of a Sunquake during the 2014 March 29 X1 Flare
Authors: Judge, Philip G.; Kleint, Lucia; Donea, Alina; Sainz Dalda,
Alberto; Fletcher, Lyndsay
Bibcode: 2014ApJ...796...85J
Altcode: 2014arXiv1409.6268J
Helioseismic data from the Helioseismic Magnetic Imager instrument have
revealed a sunquake associated with the X1 flare SOL2014-03-29T17:48
in active region NOAA 12017. We try to discover if acoustic-like
impulses or actions of the Lorentz force caused the sunquake. We
analyze spectropolarimetric data obtained with the Facility Infrared
Spectrometer (FIRS) at the Dunn Solar Telescope (DST). Fortunately,
the FIRS slit crossed the flare kernel close to the acoustic source
during the impulsive phase. The infrared FIRS data remain unsaturated
throughout the flare. Stokes profiles of lines of Si I 1082.7 nm and He
I 1083.0 nm are analyzed. At the flare footpoint, the Si I 1082.7 nm
core intensity increases by a factor of several, and the IR continuum
increases by 4% ± 1%. Remarkably, the Si I core resembles the classical
Ca II K line's self-reversed profile. With nLTE radiative models of
H, C, Si, and Fe, these properties set the penetration depth of flare
heating to 100 ± 100 km (i.e., photospheric layers). Estimates of the
non-magnetic energy flux are at least a factor of two less than the
sunquake energy flux. Milne-Eddington inversions of the Si I line show
that the local magnetic energy changes are also too small to drive the
acoustic pulse. Our work raises several questions. Have we missed the
signature of downward energy propagation? Is it intermittent in time
and/or non-local? Does the 1-2 s photospheric radiative damping time
discount compressive modes? The National Center for Atmospheric
Research is sponsored by the National Science Foundation.
Title: Solar Magnetic Reconnection at Low Altitudes and Associated
Type III Solar Radio Bursts and X-Ray Emission
Authors: Cairns, I. H.; Lobzin, V. V.; Donea, A.; Tingay, S. J.;
Oberoi, D.; Reiner, M. J.; Melrose, D. B.
Bibcode: 2014AGUFMSM13E4215C
Altcode:
Magnetic reconnection events are identified definitively in
Solar Dynamics Observatory (SDO) data on 25 September 2011, with
double-sided jets, current sheets and cusp-like geometries on top of
loops, and strong outflows at 200 km/s along pairs of open magnetic
field lines. Strong type III bursts observed by the Learmonth radio
spectrograph and imaged by the MurchisonWidefield Array (MWA) are
demonstrated to be in very good temporal and spatial coincidence
with specic SDO magnetic reconnection events and with bursts of
nonthermal 3-35 keV X-rays observed by the RHESSI spacecraft. The
reconnection sites are low, near heights of 5-10 Mm or 0.01 solar radii,
alleviating the number problem for producing the energetic electrons
and X-rays. These data, especially the images and event timings,
provide direct evidence for the long-unproven but standard model for
type III bursts: semi-relativistic electrons energized in magnetic
reconnection regions produce radio emission as they move away from the
Sun and X-rays as they move into the chromosphere. Since not all SDO
events produce X-ray or type III events, different special conditions
must exist for the production of strong radio, X-ray, or UV bursts by
reconnection events. These conditions are both on the production of
suitable energetic electrons and on the production of observable radio,
X-ray, and UV emissions from these electrons.
Title: Three-dimensional Magnetic Restructuring in Two Homologous
Solar Flares in the Seismically Active NOAA AR 11283
Authors: Liu, Chang; Deng, Na; Lee, Jeongwoo; Wiegelmann, Thomas;
Jiang, Chaowei; Dennis, Brian R.; Su, Yang; Donea, Alina; Wang, Haimin
Bibcode: 2014ApJ...795..128L
Altcode: 2014arXiv1409.6391L
We carry out a comprehensive investigation comparing the
three-dimensional magnetic field restructuring, flare energy release,
and the helioseismic response of two homologous flares, the 2011
September 6 X2.1 (FL1) and September 7 X1.8 (FL2) flares in NOAA AR
11283. In our analysis, (1) a twisted flux rope (FR) collapses onto the
surface at a speed of 1.5 km s-1 after a partial eruption
in FL1. The FR then gradually grows to reach a higher altitude and
collapses again at 3 km s-1 after a fuller eruption in
FL2. Also, FL2 shows a larger decrease of the flux-weighted centroid
separation of opposite magnetic polarities and a greater change
of the horizontal field on the surface. These imply a more violent
coronal implosion with corresponding more intense surface signatures
in FL2. (2) The FR is inclined northward and together with the ambient
fields, it undergoes a southward turning after both events. This agrees
with the asymmetric decay of the penumbra observed in the peripheral
regions. (3) The amounts of free magnetic energy and nonthermal electron
energy released during FL1 are comparable to those of FL2 within the
uncertainties of the measurements. (4) No sunquake was detected in FL1;
in contrast, FL2 produced two seismic emission sources S1 and S2 both
lying in the penumbral regions. Interestingly, S1 and S2 are connected
by magnetic loops, and the stronger source S2 has a weaker vertical
magnetic field. We discuss these results in relation to the implosion
process in the low corona and the sunquake generation.
Title: Forecasting Applications of Seismic Monitoring of the Sun's
Far Hemisphere
Authors: Lindsey, Charles; Donea, Alina-Catalina
Bibcode: 2014shin.confE.165L
Altcode:
Most of the solar influence on space weather in the terrestrial
neighborhood appears to emanate from magnetic regions in the Sun's
near hemisphere, i.e., that facing Earth. Because of solar rotation,
long-lived active regions in the far hemisphere generally rotate
into the near hemisphere within a week or two. Because of this,
space-weather forecasting over periods much exceeding a few days
can be greatly facilitated by the monitor of magnetic regions in
the Sun's far hemisphere. Computational seismic holography of the
Sun's far hemisphere provides us with such a monitor. We will review
recent improvements in seismic monitoring of the Sun's far hemisphere,
and outline prospective resources for further improvements. We will
also review developing applications of far-side seismic monitoring to
space-weather forecasting.
Title: Properties of low altitude plasma jets associated with Type
III Radio Bursts and UV to X-ray Emissions
Authors: Donea, Alina C.; Cairns, I.; Lobzin, V.; Tingay, S.; Murchison
Widefield Array Collaboration
Bibcode: 2014shin.confE..31D
Altcode:
Magnetic reconnection is still not an understood process for the
conversion of magnetic field energy into plasma motion and energised
/ heated plasma during solar events. The standard picture involves
two plasmas with antiparallel magnetic fields ≤B moving together,
resulting in a current sheet along their joint boundary. Triggered by
reconnection the magnetic field lines are changing into a different
topology. Accelerated particles escape along the new magnetic field
lines forming visible pairs of jets, with one jet on each side of each
end of the current sheet. In this work we will show a direct evidence of
magnetic reconnection events in new SDO observations of the double-sided
jets. The radio, EUV, optical and X-ray observations provide strong
evidence for the standard but long-unproven model that type III
electrons are energised in or near reconnection regions, producing radio
and X-ray emissions as they move away from and towards the Sun. Based on a large set of data from the Atmospheric Imaging Assembly
(AIA) and SECCHI instruments on NASA's SDO and STEREO B spacecraft;
radio dynamic spectra and images from the Murchison Widefield Array
(MWA), calibrated and background-subtracted dynamic spectra from the
Learmonth radio spectrograph, and RHESSI spacecraft we will discuss
the properties of the double jets.
Title: A particular seismic event generated during the solar flare
2014 March 29
Authors: Donea, Alina C.; Judge, P.; Kleint, L.; Sainz-Dalda, Alberto
Bibcode: 2014shin.confE..49D
Altcode:
The X1.3 solar flare of 2014 March 29 from AR 2017 was extremely well
observed, from both space and the ground. Helioseismic observations
from the Helioseismic Magnetic Imager (HMI) aboard the Solar Dynamics
Observatory (SDO) indicate that this flare generated a weak seismic
transient. All previous strong seismic transients to date have
emanated from sunspot penumbrae, but the source of this transient
lay outside the active-region penumbra close to a magnetic pore. Uniquely, Kleint and Sainz Dalda captured ground based imaging
and slit spectropolarimetry of this flare using the IBIS and FIRS
instruments respectively, at the Dunn Solar Telescope in Sunspot,
New Mexico. Here we report only on FIRS data along with space-based
data, IBIS data will be reported elsewhere. The FIRS infrared data
are not saturated even during the flare, which was observed through
the rise and decay phases. We are still investigating the origins of
peculiar, Zeeman-induced polarization in the He I 1083 nm multiplet. Using spectropolarimetric data of Si I and He I lines from FIRS, we
investigate the evolution of both photosphere and chromosphere above
and around the seismic source. Together with data from AIA and from
RHESSI, these data offer unique new insight into how the flare energy
is channeled into and through the photosphere into the Sun's interior
as a seismic transient. We present acoustic properties of the seismic
event and their relationship to photospheric and chromospheric plasma
and magnetic fields from FIRS, and to the evolving plasmas seen from
space from UV to X-ray wavelengths.
Title: The Role of Magnetic Fields in Transient Seismic Emission
Driven by Atmospheric Heating in Flares
Authors: Lindsey, C.; Donea, A. -C.; Martínez Oliveros, J. C.;
Hudson, H. S.
Bibcode: 2014SoPh..289.1457L
Altcode: 2013arXiv1303.3299L; 2014SoPh..tmp....9L
Transient seismic emission in flares remains largely mysterious. Its
discoverers proposed that seismic transients are driven by impulsive
heating of the flaring chromosphere. Simulations of such heating
show strong shocks, but these are damped by heavy radiative losses
as they proceed downward. Because compression of the gas the shock
enters both heats it and increases its density, the radiative losses
increase radically with the strength of the shock, leaving doubt
that sufficient energy can penetrate into the solar interior to
explain helioseismic signatures. We note that simulations to date
have no account for strong, inclined magnetic fields characteristic
of transient-seismic-source environments. A strong horizontal magnetic
field, for example, greatly increases the compressional modulus of the
chromospheric medium, greatly reducing compression of the gas, hence
radiative losses. Inclined magnetic fields, then, must be fundamental
to the role of impulsive heating in transient seismic emission.
Title: Observing the Sun with the Murchison Widefield Array
Authors: Oberoi, D.; Sharma, R.; Bhatnagar, S.; Lonsdale, C. J.;
Matthews, L. D.; Cairns, I. H.; Tingay, S. J.; Benkevitch, L.; Donea,
A.; White, S. M.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo,
R. J.; Corey, B. E.; Deshpande, A.; Emrich, D.; Gaensler, B. M.; Goeke,
R.; Greenhill, L. J.; Hazelton, B. J.; Johnston-Hollitt, M.; Kaplan,
D. L.; Kasper, J. C.; Kratzenberg, E.; Lynch, M. J.; McWhirter, S. R.;
Mitchell, D. A.; Morales, M. F.; Morgan, E.; Offringa, A. R.; Ord,
S. M.; Prabu, T.; Rogers, A. E. E.; Roshi, A.; Salah, J. E.; Udaya
Shankar, N.; Srivani, K. S.; Subrahmanyan, R.; Waterson, M.; Wayth,
R. B.; Webster, R. L.; Whitney, A. R.; William, A.; Williams, C. L.
Bibcode: 2014arXiv1403.6250O
Altcode:
The Sun has remained a difficult source to image for radio telescopes,
especially at the low radio frequencies. Its morphologically complex
emission features span a large range of angular scales, emission
mechanisms involved and brightness temperatures. In addition, time and
frequency synthesis, the key tool used by most radio interferometers to
build up information about the source being imaged is not effective for
solar imaging, because many of the features of interest are short lived
and change dramatically over small fractional bandwidths. Building on
the advances in radio frequency technology, digital signal processing
and computing, the kind of instruments needed to simultaneously capture
the evolution of solar emission in time, frequency, morphology and
polarization over a large spectral span with the requisite imaging
fidelity, and time and frequency resolution have only recently begun
to appear. Of this class of instruments, the Murchison Widefield Array
(MWA) is best suited for solar observations. The MWA has now entered
a routine observing phase and here we present some early examples from
MWA observations.
Title: Metrewave observations of the Sun
Authors: Oberoi, D.; Sharma, R.; Bhatnagar, S.; Lonsdale, C. J.;
Matthews, L. D.; Cairns, I. H.; Tingay, S. J.; Benkevitch, L.; Donea,
A.; White, S. M.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo,
R. J.; Corey, B. E.; Deshpande, A.; Emrich, D.; Gaensler, B. M.; Goeke,
R.; Greenhill, L. J.; Hazelton, B. J.; Johnston-Hollitt, M.; Kaplan,
D. L.; Kasper, J. C.; Kratzenberg, E.; Lynch, M. J.; McWhirter, S. R.;
Mitchell, D. A.; Morales, M. F.; Morgan, E.; Ord, S. M.; Prabu, T.;
Rogers, A. E. E.; Roshi, A.; Salah, J. E.; Udaya-Shankar, N.; Srivani,
K. S.; Subrahmanyan, R.; Waterson, M.; Wayth, R. B.; Webster, R. L.;
Whitney, A. R.; Williams, A.; Williams, C. L.
Bibcode: 2014ASInC..13...13O
Altcode:
High fidelity solar imaging at low radio frequencies remains a
challenge. Solar emission is characterized by its large angular size,
complex and dynamic morphological features spanning a large range of
angular sizes, emission mechanisms spanning a wide range in brightness
temperatures, and temporal and spectral variability of the emission
over large ranges in time and frequency. Capturing the solar emission
processes with high fidelity and in sufficient detail hence requires
a capability to simultaneously track the emission in time, frequency
and morphology over a large bandwidth. Traditional interferometers
rely on time and frequency synthesis to produce high fidelity and
dynamic range imaging, and are hence intrinsically poorly suited
to the task of instantaneous imaging over narrow spectral spans. With the emergence of a new generation of large-N interferometers,
the situation has improved in a very significant manner. Of these
instruments, the Murchison Widefield Array (MWA), located at the site
chosen for the SKA in Western Australia, is the one most suited for
solar observations at low radio frequencies. The MWA has recently
commenced routine observing. Here we illustrate the diversity of
features seen in solar emission using the MWA data to substantiate
its suitability for solar studies.
Title: Solar magnetic reconnection at low altitudes and associated
production of type III solar radio bursts and X-ray emission
Authors: Cairns, Iver; Reiner, Mike J.; Lobzin, Vasili; Donea, Alina;
Tingay, Steven; Oberoi, Divya
Bibcode: 2014cosp...40E.447C
Altcode:
Magnetic reconnection events are identified definitively in
Solar Dynamics Observatory (SDO) data on 25 September 2011, with
double-sided jets, current sheets and cusp-like geometries on top
of loops, and strong outflows at 200 km s (-1) along pairs of open
magnetic field lines. Strong type III bursts observed by the Learmonth
radio spectrograph and imaged by the Murchison Widefield Array (MWA)
are demonstrated to be in very good temporal and spatial coincidence
with specific SDO magnetic reconnection events and with bursts of
nonthermal 3-35 keV X-rays observed by the RHESSI spacecraft. The
reconnection sites are low, near heights of 5-10 Mm or 0.01 solar
radii, alleviating the ``number problem for producing the energetic
electrons and X-rays. These data, especially the images and event
timings, provide direct evidence for the long-unproven but standard
model for type III bursts: semi-relativistic electrons energized in
magnetic reconnection regions produce radio emission as they move away
from the Sun and X-rays as they move into the chromosphere. Since not
all SDO events produce X-ray or type III events, special conditions
must exist for the production of strong radio and X-ray bursts by
reconnection events. These conditions are both on the production of
suitable energetic electrons and on the production of observable radio
and X-ray emissions from these electrons.
Title: Computational Seismic Holography of Transient Seismic Emission
from Flares
Authors: Lindsey, C.; Donea, A. -C.; Martínez Oliveros, J. C.
Bibcode: 2013ASPC..478..323L
Altcode:
Conceived as an optimal basis for local helioseismology, computational
seismic holography applies basic principles of optics to helioseismic
signatures of waves that travel through the Sun's interior, including
its far hemisphere. Objects of its diagnostic applications include
the thermal and magnetic structure of active regions, sources of
seismic emission from the quiet Sun, active regions in the Sun's far
hemisphere, and transient seismic emission from flares. The monitor
of active regions in the Sun's far hemisphere is described by another
paper in these proceedings. This paper reviews the application of
computational seismic holography as a diagnostic of transient seismic
emission from flares.
Title: The Murchison Widefield Array: solar science with the low
frequency SKA Precursor
Authors: Tingay, S. J.; Oberoi, D.; Cairns, I.; Donea, A.; Duffin, R.;
Arcus, W.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Bunton, J. D.;
Cappallo, R. J.; Corey, B. E.; Deshpande, A.; deSouza, L.; Emrich,
D.; Gaensler, B. M.; R, Goeke; Greenhill, L. J.; Hazelton, B. J.;
Herne, D.; Hewitt, J. N.; Johnston-Hollitt, M.; Kaplan, D. L.; Kasper,
J. C.; Kennewell, J. A.; Kincaid, B. B.; Koenig, R.; Kratzenberg,
E.; Lonsdale, C. J.; Lynch, M. J.; McWhirter, S. R.; Mitchell, D. A.;
Morales, M. F.; Morgan, E.; Ord, S. M.; Pathikulangara, J.; Prabu, T.;
Remillard, R. A.; Rogers, A. E. E.; Roshi, A.; Salah, J. E.; Sault,
R. J.; Udaya-Shankar, N.; Srivani, K. S.; Stevens, J.; Subrahmanyan,
R.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.;
Williams, A.; Williams, C. L.; Wyithe, J. S. B.
Bibcode: 2013JPhCS.440a2033T
Altcode: 2013arXiv1301.6414T
The Murchison Widefield Array is a low frequency (80 - 300 MHz) SKA
Precursor, comprising 128 aperture array elements (known as tiles)
distributed over an area of 3 km diameter. The MWA is located at the
extraordinarily radio quiet Murchison Radioastronomy Observatory in
the mid-west of Western Australia, the selected home for the Phase 1
and Phase 2 SKA low frequency arrays. The MWA science goals include:
1) detection of fluctuations in the brightness temperature of the
diffuse redshifted 21 cm line of neutral hydrogen from the epoch of
reionisation; 2) studies of Galactic and extragalactic processes based
on deep, confusion-limited surveys of the full sky visible to the array;
3) time domain astrophysics through exploration of the variable radio
sky; and 4) solar imaging and characterisation of the heliosphere
and ionosphere via propagation effects on background radio source
emission. This paper concentrates on the capabilities of the MWA for
solar science and summarises some of the solar science results to date,
in advance of the initial operation of the final instrument in 2013.
Title: Enhanced sources of acoustic power surrounding AR 11429
Authors: Donea, Alina; Hanson, Christopher
Bibcode: 2013JPhCS.440a2028D
Altcode: 2013arXiv1307.1329D
Multi-frequency power maps of the local acoustic oscillations show
acoustic enhancements ("acoustic-power halos") at high frequencies
surrounding large active region. Computational seismic holography
reveals a high-frequency "acoustic-emission halo", or "seismic glory"
surrounding large active regions. In this study, we have applied
computational seismic holography to map the seismic seismic source
density surrounding AR 11429. Studies of HMI/SDO Doppler data, shows
that the "acoustic halos" and the "seismic glories" are prominent at
high frequencies 5-8 mHz. We investigate morphological properties of
acoustic-power and acoustic emission halos around an active region to
see if they are spatially correlated. Details about the local magnetic
field from vectormagnetograms of AR 11429 are included. We
identify a 15" region of seismic deficit power (dark moat) shielding
the white-light boundary of the active region. The size of the seismic
moat is related to region of intermediate magnetic field strength. The
acoustic moat is circled by the halo of enhanced seismic amplitude as
well as enhanced seismic emission. Overall, the results suggest that
features are related. However, if we narrow the frequency band to 5.5 -
6.5 mHz, we find that the seismic source density dominates over the
local acoustic power, suggesting the existence of sources that emit
more energy downward into the solar interior than upward toward the
solar surface.
Title: Statistics of Local Seismic Emission from the Solar Granulation
Authors: Lindsey, Charles; Donea, Alina-Catalina
Bibcode: 2013JPhCS.440a2044L
Altcode: 2013arXiv1307.1336L
We apply computational seismic holography to high-frequency helioseismic
observations of the quiet Sun from SDO/HMI to locate predominant
sources of seismic emission with respect to the structure of the solar
granulation. The regions of greatest seismic emission are the edges of
photospheric granules. Seismic emission from regions whose continuum
brightnesses are 95-100% of the mean, as resolved by HMI, are about
2.5 times as emissive as regions whose brightnesses are 100-104% of the
mean. The greater seismic emissivity from regions whose brightnesses are
somewhat less than the mean is roughly in line with expectations from
an understanding that attributes most seismic emission to cool plumes
plummeting from the edges of granules. However, seismic emission from
regions whose continuum brightnesses significantly exceed 104% of the
mean is also remarkably high. This unexpected feature of high-frequency
seismic emission from the solar granulation begs to be understood.
Title: Imaging the Sun with the Murchison Widefield Array
Authors: Oberoi, D.; Matthews, L. D.; Cairns, I. H.; Tingay, S. J.;
Benkevitch, L.; Donea, A.; White, S. M.; Arcus, W.; Barnes, D.;
Bernardi, G.; Bowman, J. D.; Briggs, F.; Burns, S.; Bunton, J. D.;
Cappallo, R. J.; Corey, B. E.; Deshpande, A.; deSouza, L.; Emrich,
D.; Goeke, R.; Gaensler, B. M.; Greenhill, L. -J.; Hazelton, B. J.;
Herne, D.; Johnston-Hollitt, M.; Kaplan, D. L.; Kasper, J. C.;
Kincaid, B. B.; Koeing, R.; Kratzenberg, E.; Lonsdale, C. J.; Lynch,
M. J.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.;
Ord, S. M.; Pathikulungara, J.; Prabu, T.; Remillard, R. A.; Rogers,
A. E. E.; Roshi, A.; Salah, J. E.; Sault, R. J.; Udaya-Shankar, N.;
Srivani, K. S.; Stevens, J.; Subrahmanyan, R.; Waterson, M.; Wayth,
R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.;
Wyithe, J. S. B.
Bibcode: 2013ASInC..10..131O
Altcode:
The Murchison Widefield Array (MWA) is a new generation low-frequency
radio (80--300 MHz) array. The MWA design exploits recent advances
in digital hardware capabilities and affordability of computational
capacity to meet the needs of low-frequency radio astronomy. Solar and
coronal imaging and studies of the heliosphere and the ionosphere via
their propagation effects on low-frequency radio waves comprise one of
the four key science goals of the MWA. Here we present some early solar
science results to highlight the exceptional imaging dynamic range
and fidelity of the MWA and its high time and frequency resolution,
ahead of commencement of the regular observing scheduled for mid 2013.
Title: Web-based Comprehensive Data Archive of Seismically Active
Solar Flares
Authors: Besliu-Ionescu, Diana; Donea, Alina; Cally, Paul; Lindsey,
Charles
Bibcode: 2012asst.book...31B
Altcode:
Some solar flares can release acoustic transients into the solar
subsurface of the active regions that host them. Most of the acoustic
power in these transients propagates something like 10-30 Mm beneath
the photosphere before it is refracted back to the surface, where it
raises a significant disturbance. In the strongest of these "sunquakes",
the manifestation of this transient in helio-seismic movies is an
outwardly expanding surface ripple that becomes conspicuous about
20 minutes after the impulsive phase of the flare. These "sunquakes"
offer a powerful diagnostic of wave propagation in the active region
photosphere and of the structure and dynamics of the subphotosphere. We
will present here a detailed description of our comprehensive survey
of the SOHO-MDI database for acoustic signatures from flares and the
technique used in this process. The results of the survey are presented
in a database of seismic sources generated by X and M class solar flares
during 1996-2007. It is based on a table format showing the general
characteristics of the acoustically active flares, and the times of the
solar quakes (beginning, maximum and end). The database is linked to
a composite of images of the seismic sources in different wavelengths.
Title: On The Energetics Of Seismic Excitation Mechanisms
Authors: Martinez Oliveros, Juan Carlos; Bain, H.; Krucker, S.; Donea,
A.; Hudson, H.; Lin, R. P.; Lindsey, C.
Bibcode: 2012AAS...22020503M
Altcode:
Some solar flares emit strong acoustic transients into the solar
interior during their impulsive phases (Kosovichev and Zharkova,
1998). These transients penetrate thousands of kilometers beneath the
active region photosphere and refract back to the surface, where they
produce a characteristic helioseismic signature tens of thousands
of kilometers from their origin over the succeeding hour. Several
mechanisms of seismic excitation have been proposed, ranging from
hydrodynamic shocks to Lorentz force perturbations. However, regardless
of the mechanism of generation, it is clear that not all flares induce
an acoustic response in the interior of the Sun. A concrete hypothesis
or theory about the nature of this is still a topic of ongoing
investigations. For some particular flares, we present a comparative
study between the energy deposited by the proposed mechanisms of seismic
excitation and the acoustic energy deduced using holographic techniques.
Title: Physics of Transient Seismic Emission from Flares
Authors: Lindsey, Charles A.; Donea, A.; Malanushenko, A.
Bibcode: 2012AAS...22020409L
Altcode:
We consider the physics of seismic activity in solar flares, i.e., the
release of powerful seismic transients into the solar interior during
the impulsive phases of some flares. Recent work by Hudson, Fisher,
Welsch and Bercik has attracted a great deal of positive attention
to the possible role of Lorentz-force transients in driving seismic
transient emission in flares. The implications of direct involvement
by magnetic forces in seismic transient emission, if this could be
confirmed, would be major, since magnetic fields are thought to hold
the energy source of the flares themselves. The energy invested into
acoustic transients is a small fraction of the total released by the
flare, but requires a massive impulse many times that required to
accelerate high-energy electrons into which the energy is initially
thought to be invested. What does this say about a flare mechanism that
sometimes does both? We discuss some of the outstanding diagnostic
questions that confront the recognition of magnetic-field transients
associated with Lorentz force transients based on resources HMI,
Hinode, AIA and other facilities offer us.
Title: Do We Understand Why Most Solar Flares Do Not Generate Quakes?
Authors: Donea, Alina; Lindsey, C.
Bibcode: 2012AAS...22051603D
Altcode:
While some flares release power seismic transients into the solar
interior, it is clear that only a minority of even X-class flares do
this. Strangely, some major flares of the past cycle 23 were seismically
inactive. For cycle 24, we undertake a comparative multiwavelength
analysis of a seismically powerful flare and a seismically inactive one,
to understand, observationally and physically, the basic properties
that distinguish acoustically active flares and the physics that
determines why some flares release powerful seismic transients while
others do not. Mechanisms of seismic generation will be discussed,
focusing on the roles of thick-target heating by high-energy particles,
radiative heating by white-light emission, and Lorentz-force transients.
Title: Method of cleaning images of the GONG++ network applied to
seismically active flares
Authors: Buitrago-Casas, J. C.; Alvarado, J. D.; Martinez Oliveros,
J. C.; Lindsey, C. A.; Donea, A.; Calvo-Mozo, B.
Bibcode: 2011AGUFMSH13B1935B
Altcode:
The GONG++ network has been widely used in helioseismologic
analysis. However, like it is a terrestrial observatories network
the images are highly perturbed by the atmospheric variability, doing
it some impractical to be used in helioseismic techniques on compact
regions over the solar surface. In this work we discussed briefly the
cleaning techniques on the images proposed by Lindsey and Donea (2008)
to reduce the noise caused by the atmospheric smearing but now using in
it a laplacian of nine points instead of five points, like was proposed
originally by the authors, to correct the atmospheric smearing. This
method is applied to Dopplergrams of the seismically active flares
observed by GONG and compared with those taken by SOHO/MDI and SDO/HMI.
Title: Method of cleaning images of the GONG++ netw
Authors: Buitrago-Casas, J. C.; Alvarado-Gómez, J. D.;
Martínez-Oliveros, J. C.; Lindsey, C.; Donea, A. -C.; Calvo-Mozo, B.
Bibcode: 2011sdmi.confE..30B
Altcode:
The GONG++ network has been widely used in helioseismic
analysis. However, because the GONG observatories are ground
based, its images are subject to smearing by the terrestrial
atmosphere. Temporal variations in atmospheric smearing introduce
noise in helioseismic observations of active regions. In this work,
we summarize techniques Lindsey and Donea (2008) applied to Postel
projections of GONG active-region observations to reduce this noise. We
introduce improvements based de-smearing techniques that take a warpage
in Postel projections of active regions away from disk center. We have
applied the method to GONG++ Doppler observations of seismically active
flares and compared the results with Doppler seismic observations by
SOHO/MDI and SDO/HMI.
Title: Seismic Transients from Flares in Solar Cycle 23
Authors: Donea, Alina
Bibcode: 2011SSRv..158..451D
Altcode: 2011SSRv..tmp..140D; 2011SSRv..tmp...73D; 2011SSRv..tmp..216D
Some solar flares are known to drive seismic waves into the
sub-photospheres of the magnetic regions that host them. Sunquakes,
which are identified as a wave-packet of ripples are observed on the
solar surface emanating from a focal region, known as seismic source
or sometimes as a transient. Not all seismic transients from flares
generate sunquakes. How these are produced is still a puzzle. In
this paper, I will give an overview of the observed properties of
sunquakes and efforts to understanding physics underlying them,
including numerical modelling of flare-driven oscillations.
Title: Magnetic Oscillations Mark Sites of Magnetic Transients in
an Acoustically Active Flare
Authors: Lindsey, Charles A.; Donea, A.; Hudson, H. S.; Martinez
Oliveros, J.; Hanson, C.
Bibcode: 2011SPD....42.2207L
Altcode: 2011BAAS..43S.2207L
The flare of 2011 February 15, in NOAA AR11158, was the first
acoustically active flare of solar cycle 24, and the first observed by
the Solar Dynamics Observatory (SDO). It was exceptional in a number
of respects (Kosovichev 2011a,b). Sharp ribbon-like transient Doppler,
and magnetic signatures swept over parts of the active region during
the impulsive phase of the flare. We apply seismic holography to a 2-hr
time series of HMI observations encompassing the flare. The acoustic
source distribution appears to have been strongly concentrated in a
single highly compact penumbral region in which the continuum-intensity
signature was unusually weak. The line-of-sight magnetic transient
was strong in parts of the active region, but relatively weak in
the seismic-source region. On the other hand, the neighbourhoods of
the regions visited by the strongest magnetic transients maintained
conspicuous 5-minutes-period variations in the line of sight magnetic
signature for the full 2-hr duration of the time series, before
the flare as well as after. We apply standard helioseismic control
diagnostics for clues as to the physics underlying 5-minute magnetic
oscillations in regions conducive to magnetic transients during a
flare and consider the prospective development of this property as
an indicator of flare potentiality on some time scale. We make use of
high-resolution data from AIA, using diffracted images where necessary
to obtain good photometry where the image is otherwise saturated. This
is relevant to seismic emission driven by thick-target heating in the
absence of back-warming. We also use RHESSI imaging spectroscopy to
compare the source distributions of HXR and seismic emission.
Title: Stochastic Seismic Emission from Acoustic Glories in Solar
Active Regions
Authors: Donea, Alina; Newington, Marie
Bibcode: 2011JPhCS.271a2004D
Altcode:
Helioseismic images of active regions show enhanced seismic emission in
5 mHz oscillations in a halo surrounding the active region called the
"acoustic glory". In this paper we analyse the high-frequency power
excess surrounding two active regions that occurred during the "shy"
ascending phase of the solar cycle 24, at the beginning of 2010. This
study compares the acoustic properties of seismic emission from
acoustic glories with that from the quiet Sun. The power distribution
of quiet-Sun seismic emission far from solar activity is exponential,
as for random Gaussian noise, and therefore not episodic. The magnitudes
of the acoustic glories and their seismic structure allow us to make
predictions of the seismic behaviour of active regions and compare
the data with present theoretical models.
Title: Magnetoseismic Study of the Active Region AR10720
Authors: Martínez-Oliveros, J. C.; Donea, A. -C.
Bibcode: 2009ASPC..416...81M
Altcode:
A detailed magnetoseismic analysis of the active region AR10720 on
15 January 2005 is presented. The X1.2 solar flare generated the
most powerful seismic emission discovered to date. We study the
configuration of the l-o-s magnetic field lines in the quaked area,
using extrapolations of the photospheric magnetic field (Sudol &
Harvey 2005). Temporal properties of the 6 mHz egression power maps
in the area of interest are also analysed. We then describe a number
of mechanisms believed to trigger a seismic source during a flare and
discuss the likelihood that one of these would generate a sunquake. For
this particular sunquake the McClymont effect does not seem to explain
the high seismicity of the region.
Title: Magnetic field variations and seismicity of solar active
regions
Authors: Martínez-Oliveros, J. C.; Donea, A. -C.
Bibcode: 2009MNRAS.395L..39M
Altcode: 2009arXiv0902.3856M; 2009MNRAS.tmpL.209M
Dynamical changes in the solar corona have proven to be very important
in inducing seismic waves into the photosphere. Different mechanisms
for their generation have been proposed. In this work, we explore the
magnetic field forces as plausible mechanisms to generate sunquakes
as proposed by Hudson, Fisher & Welsch. We present a spatial and
temporal analysis of the line-of-sight magnetic field variations induced
by the seismically active 2003 October 29 and 2005 January 15 solar
flares and compare these results with other supporting observations.
Title: Absorption of gamma-ray jet photons in the external photon
fields of a binary supermassive black hole system
Authors: Donea, Alina C.
Bibcode: 2008AIPC.1085..636D
Altcode:
Gamma-ray absorption due to photon-photon pair production of γ-ray
jet photons travelling in the external photon environment of a
binary supermassive black hole system is considered. We investigate
to what extent the location of a gamma-ray emitter exposed to the
anisotropic radiation field of both accretion disks affects the
gamma-ray opacity. The simple model analysed in this paper consists
of a primary black hole surrounded by a standard accretion disk in
symbiosis with a relativistic jet. The secondary black hole located
at a given position nearby has a similar mass (or smaller) and is
surrounded by a viscous Shakura-Sunyaev small accretion disk. We show
that for standard parameters of the accretion disks and a separation
distance between the two black holes of 0.05 to 0.1 pc (close system),
there is still a significant γ-ray absorption from the secondary disk.
Title: Helioseismic analysis of the solar flare-induced sunquake of
2005 January 15 - II. A magnetoseismic study
Authors: Martínez-Oliveros, J. C.; Donea, A. -C.; Cally, P. S.;
Moradi, H.
Bibcode: 2008MNRAS.389.1905M
Altcode: 2008arXiv0807.3783M; 2008MNRAS.tmp.1032M; 2008MNRAS.tmp..971M
On 2005 January 15, the active region AR10720 produced an X1.2 solar
flare that induced high levels of seismicity in the photospheric
layers. The seismic source was detected using helioseismic holography
and analysed in detail in Paper I. Egression power maps at 6 mHz, with a
2 mHz bandwidth, revealed a compact acoustic source, strongly correlated
with the footpoints of the coronal loop that hosted the flare. We
present a magnetosiesmic study of this active region to understand,
for the first time, the magnetic topological structure of a coronal
field that hosts an acoustically active solar flare. The accompanying
analysis attempts to answer questions such as: can the magnetic field
act as a barrier and prevent seismic waves from spreading away from the
focus of the sunquake? What is the most efficient magnetic structure
that would facilitate the development of a strong seismic source in
the photosphere?
Title: Mechanics of Seismic Emission from Solar Flares
Authors: Lindsey, C.; Donea, A. -C.
Bibcode: 2008SoPh..251..627L
Altcode: 2008SoPh..tmp...49L
Instances of seismic transients emitted into the solar interior
in the impulsive phases of some solar flares offer a promising
diagnostic tool, both for understanding the physics of solar flares
and for the general development of local helioseismology. Among
the prospective contributors to flare acoustic emission that have
been considered are: i) chromospheric shocks propelled by pressure
transients caused by impulsive thick-target heating of the upper
and middle chromosphere by high-energy particles, ii) heating of the
photosphere by continuum radiation from the chromosphere or possibly
by high-energy protons, and iii) magnetic-force transients caused by
magnetic reconnection. Hydrodynamic modeling of chromospheric shocks
suggests that radiative losses deplete all but a small fraction of
the energy initially deposited into them before they penetrate the
photosphere. Comparisons between the spatial distribution of acoustic
sources, derived from seismic holography of the surface signatures of
flare acoustic emission, and the spatial distributions of sudden changes
both in visible-light emission and in magnetic signatures offer a
possible means of discriminating between contributions to flare acoustic
emission from photospheric heating and magnetic-force transients. In
this study we develop and test a means for estimating the seismic
intensity and spatial distribution of flare acoustic emission from
photospheric heating associated with visible-light emission and compare
this with the helioseismic signatures of seismic emission. Similar
techniques are applicable to transient magnetic signatures.
Title: Seismic Emissions from a Highly Impulsive M6.7 Solar Flare
Authors: Martínez-Oliveros, J. C.; Moradi, H.; Donea, A. -C.
Bibcode: 2008SoPh..251..613M
Altcode: 2008arXiv0801.0898M; 2008SoPh..tmp...20M
On 10 March 2001 the active region NOAA 9368 produced an unusually
impulsive solar flare in close proximity to the solar limb. This
flare has previously been studied in great detail, with observations
classifying it as a type 1 white-light flare with a very hard spectrum
in hard X-rays. The flare was also associated with a type II radio burst
and coronal mass ejection. The flare emission characteristics appeared
to closely correspond to previous instances of seismic emission from
acoustically active flares. Using standard local helioseismic methods,
we identified the seismic signatures produced by the flare that, to
date, is the least energetic (in soft X-rays) of the flares known to
have generated a detectable acoustic transient. Holographic analysis of
the flare shows a compact acoustic source strongly correlated with the
impulsive hard X-rays, visible continuum, and radio emission. Time -
distance diagrams of the seismic waves emanating from the flare region
also show faint signatures, mainly in the eastern sector of the active
region. The strong spatial coincidence between the seismic source
and the impulsive visible continuum emission reinforces the theory
that a substantial component of the seismic emission seen is a result
of sudden heating of the low photosphere associated with the observed
visible continuum emission. Furthermore, the low-altitude magnetic loop
structure inferred from potential-field extrapolations in the flaring
region suggests that there is a significant anti-correlation between
the seismicity of a flare and the height of the magnetic loops that
conduct the particle beams from the corona.
Title: A Comparison of the Acoustic Hardness of Acoustically Active
and Non-Active Solar Flares
Authors: Beşliu-Ionescu, Diana; Donea, Alina; Cally, Paul
Bibcode: 2008AIPC.1043..252B
Altcode:
Recent corrections to some of the GONG+intensity images of flares allow
us to image the acoustic power of white light flare signatures. The
images clearly show compact regions of white light power at 6 mHz,
which are well correlated spatially with the seismic signatures of the
flares, when the flare proved to be acoustically active. It has been a
puzzle why some of the white light flares, mainly very strong flares,
did not induced any seismic waves into the photosphere. We believe
that a comparison of the white light spectral hardness of two flares
(one seismically active and another one seismically quiet) is the clue
to understand the physics of the sun quakes.
Title: HXR photospheric footprints
Authors: Martínez-Oliveros, J. C.; Donea, A. -C.; Cally, P. S.
Bibcode: 2008IAUS..247..110M
Altcode: 2007IAUS..247..110M
We have analysed the 6 mHz egression power signatures of some
accoustically active X-class solar flares. During the impulsive
phase these flares produced conspicuous seismic signatures which
have kernel-like structures, mostly aligned with the neutral line of
the host active region. The kernel-like structures show the effect
of constructive interference of the acoustic waves emanating from
the complex sources, suggesting motion of the acoustic sources. The
co-aligment between the seismic signatures and the hard X-ray emission
observed by RHESSI from the footpoints of the coronal loops suggests
a direct link between relativistic particles accelerated during the
flare and the hydrodynamic response of the photosphere during flares.
Title: Correlative study of the emission from flares associated with
Sun quakes
Authors: Martínez-Oliveros, J. C.; Donea, A. -C.; Cally, P. S.
Bibcode: 2008IAUS..247...99M
Altcode: 2007IAUS..247...99M
Multi-wavelength studies of energetic solar flares with seismic
emissions have revealed interesting common features that may help us
to identify the correlations of flare signatures from the inner to
the outer solar atmosphere and, to develop diagnostic techniques to
aid in the sun quake detection. In our study, we make use the relation
between the microwave and the hard X-ray emissions associated with such
flares to propose a scenario for the ignition of seismic transients
from flares. We explore the mechanisms of energy transport to the
photosphere, such us back-warming or direct particle impacts.
Title: Recent Developments in Solar Quakes Studies
Authors: Bešliu-Ionescu, D.; Donea, A. -C.; Cally, P.; Lindsey, C.
Bibcode: 2008ASPC..383..297B
Altcode:
Observations in hard and soft X-rays, chromospheric lines, and the
visible continuum, together with helioseismic observations, make
it possible to model the 3-dimensional profile of a sunquake from
the corona into the subphotosphere of the active region that hosts
the flare. Chromospheric line observations show us the part of the
solar atmosphere where high-energy electrons are thought to cause
thick-target heating that causes intense white-light emission and
drives seismic waves into the active region subphotosphere. We have
made a preliminary analysis of observations for some of the strongest
acoustically noisy flares, including spectral observations in line
NaD1 (586.9 nm) and line-center observations in Hα. Hα line-center
observations will be shown for other sunquakes in Solar Cycle 23. Hinode
will give us especially high-resolution chromospheric-line observations
of acoustically active flares in Solar Cycle 24.
Title: From Gigahertz to Millihertz: A Multiwavelength Study of the
Acoustically Active 14 August 2004 M7.4 Solar Flare
Authors: Martínez-Oliveros, J. C.; Moradi, H.; Besliu-Ionescu, D.;
Donea, A. -C.; Cally, P. S.; Lindsey, C.
Bibcode: 2007SoPh..245..121M
Altcode: 2007arXiv0707.2019M
We carried out an electromagnetic acoustic analysis of the solar
flare of 14 August 2004 in active region AR10656 from the radio to the
hard X-ray spectrum. The flare was a GOES soft X-ray class M7.4 and
produced a detectable sun quake, confirming earlier inferences that
relatively low energy flares may be able to generate sun quakes. We
introduce the hypothesis that the seismicity of the active region is
closely related to the heights of coronal magnetic loops that conduct
high-energy particles from the flare. In the case of relatively short
magnetic loops, chromospheric evaporation populates the loop interior
with ionised gas relatively rapidly, expediting the scattering of
remaining trapped high-energy electrons into the magnetic loss cone and
their rapid precipitation into the chromosphere. This increases both
the intensity and suddenness of the chromospheric heating, satisfying
the basic conditions for an acoustic emission that penetrates into
the solar interior.
Title: Chromospheric Line Emission Analysis of the July 16, 2004
Sun Quake
Authors: Beşliu-Ionescu, Diana; Donea, Alina; Cally, Paul; Lindsey,
Charles
Bibcode: 2007AIPC..934...38B
Altcode:
Observations in chromospheric lines and the visible continuum together
with photospheric helioseismic measurements make possible to image a
3-dimensional profile of a sun quake in a flaring region. Chromospheric
line observations show us the part of the solar atmosphere where
high-energy electrons are thought to cause thick target heating that
then could also cause intense white-light emission and could drive
seismic waves into the active region subphotosphere, we present here
the preliminary results of the sun quake of July 16, 2004.
Title: Outstanding results of Romanian solar physics research in
the frame of international cooperation and PhD grants abroad
Authors: Besliu-Ionescu, D.; Donea, A. C.; Maris, G.; Mierla, M.;
Moise, E.; Popescu, M. D.
Bibcode: 2007AIPC..895...38B
Altcode:
The valuable results of the Romanian solar physics group in different
fields of solar and solar-terrestrial researches are revised. A
new index, Qx, was defined by us in order to give an evaluation of
the Soft X-Ray (SXR) flare energy, similarly to the Q index for Hα
flares. Seismic emission from solar flares is distinguished by its
origin in plain view above the photosphere, as opposed to convective
emission, which is hidden beneath the photosphere. To understand
the physics of the acoustic radiation responsible for solar quakes
a systematic survey covering a large number of X-class and some
M-class solar flares observed by SOHO/MDI during 1996 and 2006 has
been undertaken. A number of papers present the dynamics of the solar
corona in the minimum phase (1996) and during the ascending phase (1998)
of the solar cycle, using spectral data of LASCO-C1/SoHO experiment. In
particular, the emergence of the slow solar wind at the above mentioned
solar cycle phases was studied. A series of contributions subscribe to
ongoing efforts to resolve plasma's fine-scale structure and dynamics
at the base of coronal holes, aiming to better identify the fast solar
wind origin in low solar atmosphere. Data from the highest resolution
solar spectrograph, SUMER/SoHO, in EUV emission lines from transition
region and corona were analyzed. We have also analyzed the cyclic
distribution of high-speed streams in solar wind during the 1964-1996
interval (Solar Cycles nos. 20-22) as compared to the classical aspect
of the 11-year cycle by sunspot relative numbers (Wolf numbers). The
presence in heliosphere of the cool neutral Helium, among the other
interstellar neutrals, was analyzed. The neutrals are ionized by charge
exchange, photo ionization, and electron impact. Helium is focused by
the Sun's gravitational field on the downwind side.
Title: Helioseismic analysis of the solar flare-induced sunquake of
2005 January 15
Authors: Moradi, H.; Donea, A. -C.; Lindsey, C.; Besliu-Ionescu, D.;
Cally, P. S.
Bibcode: 2007MNRAS.374.1155M
Altcode: 2007arXiv0704.3472M; 2006MNRAS.tmp.1369M
We report the discovery of one of the most powerful sunquakes
detected to date, produced by an X1.2-class solar flare in active
region AR10720 on 2005 January 15. We used helioseismic holography
to image the source of seismic waves emitted into the solar interior
from the site of the flare. Acoustic egression power maps at 3 and 6
mHz with a 2-mHz bandpass reveal a compact acoustic source strongly
correlated with impulsive hard X-ray and visible-continuum emission
along the penumbral neutral line separating the two major opposing
umbrae in the δ-configuration sunspot that predominates AR10720. At 6
mHz the seismic source has two components, an intense, compact kernel
located on the penumbral neutral line of the δ-configuration sunspot
that predominates AR10720, and a significantly more diffuse signature
distributed along the neutral line up to ~15 Mm east and ~30 Mm west
of the kernel. The acoustic emission signatures were directly aligned
with both hard X-ray and visible continuum emission that emanated
during the flare. The visible continuum emission is estimated at 2.0
× 1023 J, approximately 500 times the seismic emission
of ~4 × 1020 J. The flare of 2005 January 15 exhibits
the same close spatial alignment between the sources of the seismic
emission and impulsive visible continuum emission as previous flares,
reinforcing the hypothesis that the acoustic emission may be driven
by heating of the low photosphere. However, it is a major exception
in that there was no signature to indicate the inclusion of protons
in the particle beams thought to supply the energy radiated by the
flare. The continued strong coincidence between the sources of seismic
emission and impulsive visible continuum emission in the case of a
proton-deficient white-lightflare lends substantial support to the
`back-warming' hypothesis, that the low photosphere is significantly
heated by intense Balmer and Paschen continuum-edge radiation from
the overlying chromosphere in white-light flares.
Title: Study of the Seismically Active Flare of July 16, 2004
Authors: Besliu-Ionescu, D.; Donea, A. C.; Cally, P.; Lindsey, C.
Bibcode: 2007RoAJ...17S..83B
Altcode:
Sunquakes have proven to be the most powerful events occurring at the
solar surface. They are triggered by the impulsive flares produced
in the corona, just above the acoustically active regions. Not
every impulsive flare produces seismic waves emanating from the
highly depressed photosphere, just beneath the flare. So far, we
have identified a few mechanisms which can deliver acoustic energy
into the photosphere: 1) the back-warming radiation suddenly heating
the photosphere; 2) a strong shock-like compression wave propagating
downwards into the chromosphere; 3) relativistic particles delivering
directly the energy and momentum into the photosphere; and, 4)
probably the magnetic tension at the feet of the loops. In order to
discriminate which of these is the most efficient or dominated during a
particular acoustically active flare, we have analysed the coronal and
chromospheric emission of the regions just above the seismic source. We
have performed a multiwavelength analysis of the active region 10649
that hosted the acoustically active solar flare of July 16, 2004. The
spatial coincidence between the emissions at different layers of the
sun, from the photosphere to the corona, suggests that high-energy
particles travel through the coronal layers from the reconnection
site, hit the solar chromosphere warming it up, which then, responds
by sending further into the photosphere enough energy (carried either
by the shock wave or by the Balmer and Pachen radiation) to produce
a seismic event.
Title: Chromospheric line emission in seismically active flares
Authors: Beşliu-Ionescu, D.; Donea, A. -C.; Lindsey, C.; Cally, P.;
Mariş, G.
Bibcode: 2007AdSpR..40.1921B
Altcode:
Some flares are known to drive seismic transients into the solar
interior. The effects of these seismic transients are seen in
helioseismic observations of the Sun's surface thousands of km
from their sources in the hour succeeding the impulsive phase of
the flare. Energetic particles impinging from the corona into the
chromosphere are known to drive strong, downward-propagating shocks in
active region chromospheres during the impulsive phases of flares. Hα
observations have served as an important diagnostic of these shocks,
showing intense emission with characteristic transient redshifts. In
most flares no detectable transients penetrate beneath the active region
photosphere. In those that do, there is a strong correlation between
compact white-light emission and the signature of seismic emission. This
study introduces the first known Hα observations of acoustically active
flares, centered in the core of the line. The morphology of line-core
emission Hα in the impulsive phase of the flare is similar to that
of co-spatial line-core emission in NaD 1, encompassing
the site of seismic emission but more extended. The latter shows a
compact red shift in the region of seismic emission, but a similar
feature is known to appear in a conjugate magnetic footpoint from
which no seismic emission emanates. Radiative MHD modelling based
on the profiles of chromospheric line emission during the impulsive
phases of flares can contribute significantly to our understanding of
the mechanics of flare acoustic emission penetrating into the solar
interior and the conditions under which it occurs.
Title: New Detection of Acoustic Signatures from Solar Flares
Authors: Donea, A. C.; Besliu-Ionescu, D.; Cally, P.; Lindsey, C.
Bibcode: 2006ASPC..354..204D
Altcode:
With the advancement of local helioseismic techniques such as
helioseismic holography we have now detected numerous seismic sources
of varying size and intensity produced by solar flares. We have
performed a systematic survey of the SOHO-MDI database in search for
seismic waves from X-class flares produced during 1996 -- 2005. The
detection of acoustically active flares has opened a new and
promising connection between helioseismology and flare physics. The
main question we ask is: why are some large flares acoustically active
while most are acoustically inactive? We also address questions
such as: Is photospheric heating by high-energy protons a major factor
in seismic emission from flares? What is the effect of magnetic fields
in the acoustics of a flare?
Title: Simulations of Acoustic Excitation
Authors: Lindsey, C.; Birch, A. C.; Donea, A. -C.
Bibcode: 2006ASPC..354..174L
Altcode:
Acoustic emission from solar granulation is thought to be relatively
localized and episodic, emanating largely as relatively discrete
wavepackets emitted from convective plumes falling into the solar
interior from near-surface layers at which granular convection
takes place. We devise preliminary simulated sound computations to
characterize the range of acoustic signatures that can be expected
from random localized emission for a range of surface densities and
mean episodic frequencies. In the simple models studied here wave
excitation is represented by dipole emitters at a depth of one~Mm
randomly distributed in time and location over the surface of a standard
solar model. We apply holographic regressions to the resulting surface
acoustic fields and compile acoustic power statistics on the resulting
helioseismic signatures. Acoustic power statistics of random, stationary
Gaussian noise are characterized by an exponential distribution. The
relatively localized and episodic nature of acoustic emission expected
from downfalling plumes should be distinguishable from Gaussian noise
by a characteristic deviation from the exponential distribution. If the
episodes are relatively dense and frequent compared to the temporal and
spatial discrimination of the helioseismic diagnostics, the deviation
from Gaussian statistics becomes small. Simulations of acoustic
emission, then, allow us to assess the potential of local helioseismic
diagnostics for recognizing episodic excitation of acoustic waves.
Title: Seismic Emission from A M9.5-Class Solar Flare
Authors: Donea, A. -C.; Besliu-Ionescu, D.; Cally, P. S.; Lindsey,
C.; Zharkova, V. V.
Bibcode: 2006SoPh..239..113D
Altcode: 2006SoPh..tmp...65D
Following the discovery of a few significant seismic sources at
6.0 mHz from the large solar flares of October 28 and 29, 2003, we
have extended SOHO/MDI helioseismic observations to moderate M-class
flares. We report the detection of seismic waves emitted from the β
γ δ active region NOAA 9608 on September 9, 2001. A quite impulsive
solar flare of type M9.5 occurred from 20:40 to 20:48 UT. We used
helioseismic holography to image seismic emission from this flare into
the solar interior and computed time series of egression power maps
in 2.0 mHz bands centered at 3.0 and 6.0 mHz. The 6.0 mHz images show
an acoustic source associated with the flare some 30 Mm across in the
East - West direction and 15 Mm in the North - South direction nestled
in the southern penumbra of the main sunspot of AR 9608. This coincides
closely with three white-light flare kernels that appear in the sunspot
penumbra. The close spatial correspondence between white-light and
acoustic emission adds considerable weight to the hypothesis that the
acoustic emission is driven by heating of the lower photosphere. This
is further supported by a rough hydromechanical model of an acoustic
transient driven by sudden heating of the low photosphere. Where direct
heating of the low photosphere by protons or high-energy electrons is
unrealistic, the strong association between the acoustic source and
co-spatial continuum emission can be regarded as evidence supporting
the back-warming hypothesis, in which the low photosphere is heated
by radiation from the overlying chromosphere. This is to say that a
seismic source coincident with strong, sudden radiative emission in the
visible continuum spectrum indicates a photosphere sufficiently heated
so as to contribute significantly to the continuum emission observed.
Title: Magnetohelioseismic Analysis of AR10720 Using Helioseismic
Holography
Authors: Moradi, H.; Donea, A.; Besliu-Ionescu, D.; Cally, P.; Lindsey,
C.; Leka, K.
Bibcode: 2006ASPC..354..168M
Altcode:
We report on the recent discovery of one of the most powerful sunquakes
detected to date produced by the January 15, 2005 X1.2 solar flare
in active region 10720. We used helioseismic holography to image the
acoustic source of the seismic waves produced by the flare. Egression
power maps at 6 mHz with a 2 mHz bandwidth reveal a strong, compact
acoustic source correlated with the footpoints of a coronal loop
that hosted the flare. Using data from various solar observatories,
we present a comprehensive analysis of the acoustic properties of
the sunquake and investigate the role played by the configuration of
the photospehric magnetic field in the production of flare generated
sunquakes.
Title: Seismic emission from M-class solar flares
Authors: Besliu-Ionescu, D.; Donea, A. -C.; Cally, P.; Lindsey, C.
Bibcode: 2006ESASP.624E..67B
Altcode: 2006soho...18E..67B
No abstract at ADS
Title: The acoustically active solar flare of 2005 January 15
Authors: Moradi, H.; Donea, A. -C.; Lindsey, C.; Besliu-Ionescu, D.;
Cally, P. S.
Bibcode: 2006ESASP.624E..66M
Altcode: 2006soho...18E..66M
No abstract at ADS
Title: Seismic Radiation from M-class Solar Flares
Authors: Besliu-Ionescu, Diana; Donea, Alina-C.; Cally, Paul; Lindsey,
Charles
Bibcode: 2006IAUS..233..385B
Altcode:
Helioseismic holography is a technique used to image the sources
of seismic disturbances observed at the solar surface. It has been
used to detect acoustic emission, known as sun quakes, radiated from
X-class solar flares. Since the seismic power emitted by the X-class
flares has proved to be independent of the strength of the flare,
we have undertaking a systematic search for seismic signatures from
M-class solar flares, observed by SOHO-MDI.We have detected significant
acoustic emission from a few M-class solar flares. Preliminary results
of the survey of M-type solar flares studied so far is available at:
aira.astro.ro/~deanna/M.html.
Title: Significant Acoustic Activity in AR10720 on January 15, 2005
Authors: Beşliu-Ionescu, D.; Donea, A. -C.; Cally, P.; Lindsey, C.
Bibcode: 2006RoAJ...16S.203B
Altcode: 2006RoAJS..16..203B
We report the recent discovery of one of the most acoustically powerful
flare detected to date produced by the January 2005 2005, X1.2 solar
flare in AR10720. We used helioseismic holography to image the acoustic
source of the seismic waves produced by the flare. Egression Power maps
at 6 mHz show a strong, extended acoustic signature which is the focus
of the solar quake. At approximately 20 minutes after the appearance
of the flare signature, we could also see the seismic response of
the photosphere to the energy deposited by the flare in the form of
"ripples" on the solar surface.
Title: a Survey of X-Class Solar Flares during 2001 and 2002 IN
Search for Seismic Radiation
Authors: Besliu-Ionescu, D.; Donea, A. -C.; Cally, P.; Lindsey, C.
Bibcode: 2005ESASP.600E.111B
Altcode: 2005ESPM...11..111B; 2005dysu.confE.111B
No abstract at ADS
Title: Seismic Emission from the Solar Flares of 2003 October 28
and 29
Authors: Donea, A. -C.; Lindsey, C.
Bibcode: 2005ApJ...630.1168D
Altcode:
We report the detection of seismic waves emitted from powerful solar
flares that occurred in NOAA Active Region 10486 on 2003 October 28 and
29. We used helioseismic holography to image the seismic sources of
the waves. This technique was previously used to image the source of
seismic emission from the large solar flare of 1996 July 9. Egression
power maps at 6 mHz with a 2 mHz bandwidth reveal multiple compact
acoustic sources strongly associated with the footpoints of a coronal
loop that hosted the flares. The total acoustic energy in the flare
signatures is a very small fraction of the total energy radiated by
the flares. The acoustic signatures are co-aligned with hard X-ray
signatures, suggesting a direct link between energetic particles
accelerated during the flare and the acoustic waves as a hydrodynamic
response of the chromosphere, or possibly the underlying photosphere,
to these particles at the footpoints of the loop. There is also
evidence of high-energy protons impinging onto the chromosphere in
the neighborhoods of the acoustic sources. Observations of emission
in the D1 line of neutral sodium at the onset of the October 29 flare
show evidence of a downward-propagating shock/condensation at the
onset of the flare. Concurrent Global Oscillation Network Group (GONG)
intensity observations show significant radiative emission with a sudden
onset in the compact region encompassing the acoustic signature. Most
flares appear to be acoustically inactive. Photospheric heating by
high-energy protons is likely to be a major factor in seismic emission
from acoustically active flares.
Title: Seismic Emission From Solar Flares
Authors: Lindsey, C. A.; Donea, A.
Bibcode: 2005AGUSMSP24A..06L
Altcode:
Local helioseismic diagnostics applied to helioseismic observations from
the Michelson Doppler Imager (MDI) on the Solar Heliospheric Observatory
(SOHO) have shown the clear signature of seismic emission from three
flares during the advent of SOHO. All three of these flares showed the
signatures of γ-ray emission indicating the involvement of accelerated
protons. Two of the acoustically active flares were recent, October 28
and 29 of 2003, and were observed by RHESSI. In both of these instances,
the sources of the acoustic emission acoustic source, determined by
computational seismic holography, coincided closely with compact γ -ray
signatures of protons. Elementary considerations ofenergy and momentum
transfer appear to make chromospheric and photospheric heating by
protons favorable for seismic emission from flares. If this is actually
the case, proton diagnostics of flares from RHESSI would be useful for
identifying acoustically active flares for the Helioseismic Magnetic
Imager (HMI) on the Solar Dynamics Observatory (SDO), and possibly for
the SOHO/MDI. Given a clear understanding of the effects of flares on
Doppler signatures in active regions, acoustic emission from flares can
give us a powerful control utility for seismic diagnostics of active
regions subphotospheres. This research has benefitted greatly from
the keen insights of Valentina Zharkova, Gerald Share, Hugh Hudson,
and Sam Krucker. It has been supported by grants from the Living with
a Star and Supporting Research and Technology programs of the National
Aeronautics and Space Administration and the Stellar Astronomy and
Astrophysics branch of the National Science Foundation.
Title: Modeling Seismic Emission in the Quiet Sun
Authors: Lindsey, C. A.; Birch, A. C.; Donea, A.; Rast, M. P.
Bibcode: 2005AGUSMSP13A..06L
Altcode:
A major issue in the physics of seismic emission in the quiet Sun
is the degree to which the emission from any particular location is
episodic. Given our present understanding, this question is equivalent
to that of how localized the sources of emission are at any particular
moment. A variety of statistical tools are available to address
this issue. For example, if seismic emission can be characterized
in terms of relatively infrequent episodes sparsely distributed,
then the distribution in amplitude of the source terms over space and
time should be non-Gaussian. If the episodes of emission are densely
disseminenated in space and time such that many phase-independent
episodes would be expected in a space-time resolution element,then
the distribution in amplitude approaches Gaussian statistics, and
the distribution in power becomes exponential. Computational seismic
holography focused at the solar surface from a subjacent vantage
makes it possible to image acoustic sources and do statistics on the
seismic source term. Earlier work by Donea, Lindsey and Braun, based on
holographic imaging of acoustic sources, failed to detect a departure of
source amplitudes from Gaussian statistics. This suggests that seismic
sources are relatively dense on a spatial scale of 3~Mm and a temporal
scale of 10~min. What this means in terms of the physics of acoustic
excitation requires modeling. We will describe beginning efforts to
model seismic emission in a standard model of the solar subphotosphere
in terms of randomly distributed dipoles located close to the solar
surface. A significant departute of the source amplitude distribution
from Gaussian statistics is of fundamental importance to the utility
of local helioseismic diagnostics to seismic emission in the quiet Sun.
Title: Simultaneous Magnetic Field Time Series in AR10486 and AR10488
During the Period October 29--31, 2003
Authors: Beşliu, Diana; Donea, Alina-Catalina; Cally, Paul; Maris,
Georgeta
Bibcode: 2005RoAJ...15...33B
Altcode:
No abstract at ADS
Title: Seismic Waves from the Solar Flares of 2003 October 28 and 29
Authors: Donea, A. -C.; Lindsey, C.
Bibcode: 2004ESASP.559..152D
Altcode: 2004soho...14..152D
No abstract at ADS
Title: M 87 as a misaligned synchrotron-proton blazar
Authors: Reimer, A.; Protheroe, R. J.; Donea, A. -C.
Bibcode: 2004A&A...419...89R
Altcode:
The giant radio galaxy M 87 is usually classified as a Fanaroff-Riley
class I source, suggesting that M 87 is a mis-aligned BL Lac object. Its
unresolved nuclear region emits strong non-thermal emission from radio
to X-rays which has been interpreted as synchrotron radiation. In
an earlier paper we predicted M 87 as a source of detectable gamma
ray emission in the context of the hadronic Synchrotron-Proton Blazar
(SPB) model. The subsequent tentative detection of TeV energy photons
by the HEGRA-telescope array would, if confirmed, make it the first
radio galaxy to be detected at TeV-energies. We discuss the emission
from the unresolved nuclear region of M 87 in the context of the
SPB model, and give examples of possible model representations of its
non-simultaneous spectral energy distribution. The low-energy component
can be explained as synchrotron radiation by a primary relativistic
electron population that is injected together with energetic protons
into a highly magnetized emission region. We find that the γ-ray
power output is dominated either by μ±/π±
synchrotron or proton synchrotron radiation depending on whether the
primary electron synchrotron component peaks at low or high energies,
respectively. The predicted γ-ray luminosity peaks at ∼100 GeV at a
level comparable to that of the low-energy hump, and this makes M 87 a
promising candidate source for the newly-commissioned high-sensitivity
low-threshold Cherenkov telescopes H.E.S.S., VERITAS, MAGIC and
CANGAROO III. Because of its proximity, the high-energy spectrum of M
87 is unaffected by absorption in the cosmic infrared (IR) background
radiation field, and could therefore serve as a template spectrum
for the corresponding class of blazar if corrected for mis-alignment
effects. This could significantly push efforts to constrain the cosmic
IR radiation field through observation of more distant TeV-blazars,
and could have a strong impact on blazar emission models. If M 87
is a mis-aligned BL-Lac object and produces TeV-photons as recently
detected by the HEGRA-array, in the context of the SPB model it must
also be an efficient proton accelerator.
Title: M87 - a misaligned synchrotron-proton blazar?
Authors: Reimer, A.; Protheroe, R. J.; Donea, A. -C.
Bibcode: 2004NewAR..48..411R
Altcode: 2004astro.ph..2258R
The Fanaroff-Riley (FR) class 1 radio galaxy M87 is widely believed to
be a misaligned blazar of BL Lac type. Its unresolved nuclear region
is a strong non-thermal emitter of radio to X-ray photons that have
been interpreted as synchrotron radiation. The recent detection of
TeV-photons by the HEGRA-telescope array, if confirmed, would make
it the first radio galaxy detected at TeV-energies. We discuss M87's
core emission in the context of the hadronic Synchrotron-Proton Blazar
model. By modeling M87's non-simultaneous spectral energy distribution
we predict the peak power of the γ-ray component at ∼100 GeV at
a flux level detectable for the new Cherenkov telescopes H.E.S.S.,
VERITAS and MAGIC. Thanks to M87's proximity TeV photon absorption in
the cosmic background radiation field is negligible. This offers for
the first time the opportunity to directly trace the intrinsic high
energy cutoff of a TeV-emitting blazar-like object.
Title: Two days in the life of AR10486
Authors: Donea, A. -C.; Maris, G.; Lindsey, C. A.
Bibcode: 2004IAUS..223..241D
Altcode: 2005IAUS..223..241D
Magnetic and acoustic properties of the complex active region AR 486
are analyzed for two consecutive days: October 28 and October 29,
2003 when two large flares of magnitude X17.2 and X10 were produced,
respectively. Using the technique of helioseismic holography we detected
seismic waves emitted from these flares at 6 mHz. SOHO-MDI white light
images, magnetograms, and Dopplergrams are used to study the physics
of the acoustic sources.
Title: TeV γ-rays and cosmic rays from the nucleus of M87, a
mis-aligned BL Lac object
Authors: Protheroe, R. J.; Donea, A. -C.; Reimer, A.
Bibcode: 2003APh....19..559P
Altcode: 2002astro.ph.10249P
The unresolved nuclear region of M87 emits strong non-thermal
emission from radio to X-rays. Assuming this emission to originate
in the pc scale jet aligned at θ∼30° to the line of sight, we
interpret this emission in the context of the synchrotron proton
blazar model. We find the observed nuclear jet emission to be
consistent with M87 being a mis-aligned BL Lac object and predict
γ-ray emission extending up to at least 100 GeV at a level easily
detectable by GLAST and MAGIC, and possibly by VERITAS depending
on whether it is high-frequency or low-frequency peaked. Predicted
neutrino emission is below the sensitivity of existing and planned
neutrino telescopes. Ultra-high-energy neutrons produced in pion
photoproduction interactions decay into protons after escaping from
the host galaxy. Because energetic protons are deflected by the
intergalactic magnetic field, the protons from the decay of neutrons
emitted in all directions, including along the jet axis where the
Doppler factor and hence emitted neutron energies are higher, can
contribute to the observed ultra-high-energy cosmic rays. We consider
the propagation of these cosmic ray protons to Earth and conclude that
M87 could account for the observed flux if the extragalactic magnetic
field topology were favourable.
Title: M87 as a Misaligned Synchrotron-Proton Blazar
Authors: Reimer, Anita; Protheroe, R. J.; Donea, A. -C.
Bibcode: 2003ICRC....5.2631R
Altcode: 2003ICRC...28.2631R
In the framework of the unified model for radio-loud Active Galactic
Nuclei (AGN) the Fanaroff-Riley (FR) class 1 radio galaxy M87 is a
misaligned blazar of BL Lac type. Its unresolved nuclear region is
a strong non-thermal emitter of radio to X-ray photons that have
been interpreted as synchrotron radiation. The recent detection of
TeV-photons by the HEGRA-telescope array, if confirmed, would make
it the first radio galaxy detected at TeV-energies. We discuss the
emission from the core region of M87 in the context of the hadronic
SynchrotronProton Blazar (SPB) model, and place constraints on the
model's parameter space consistent with this HEGRA-detection. model
fits to M87's non-simultanous spectral energy distribution (SED)
predict the peak power of the γ -ray component at ∼100 GeV at a
level comparative to the low-energy hump. This makes M87 a promising
target for e.g. H.E.S.S., VERITAS and MAGIC.
Title: Cosmic Rays from the Nucleus of M87
Authors: Donea, Alina C.; Protheroe, R. J.; Reimer, A.
Bibcode: 2003ICRC....2..695D
Altcode: 2003ICRC...28..695D
The unresolved nuclear region of M87 emits strong non-thermal emission
from radio to X-rays, and this has been interpreted as jet emission
from a misaligned BL Lac object in the context of the Synchrotron
Proton Blazar (SPB) model (Prothero e et al 2003). In this model
extragalactic cosmic rays are generated as neutrons produced in pion
photopro duction interactions decaying into protons after escaping
from the host galaxy. Because energetic protons are deflected by the
intergalactic magnetic field, the protons from the decay of neutrons
emitted in all directions, including along the jet axis where the
Doppler factor and hence emitted neutron energies are higher, can
contribute to the observed ultra-high energy cosmic rays. We consider
the propagation of these cosmic ray protons to Earth and conclude that
M87 could account for the observed flux if the extragalactic magnetic
field top ology were favourable.
Title: Absorption of GeV and TeV g-Rays in M87 and 3C 273
Authors: Donea, Alina C.
Bibcode: 2003ICRC....5.2671D
Altcode: 2003ICRC...28.2671D
M87 and 3C273 are famous AGN with powerful jets. High energy gammaray
emission from these jets has been calculated [10,11] with hadronic
models in which accelerated protons interact with internal radiation
(synchrotron) and/or external radiation fields. Leptonic models have
also been used to model the gamma-ray emission of both objects[1]. GeV
to TeV gamma-rays produced in the jets may or may not be absorb ed
by γ -γ pair production in the radiation fields of the accretion
disk and torus. We investigate this problem for M87 and 3C 273. In
the case of M87, a mis-aligned BL Lac object, there appears to be a
deficiency in dust at parsec scales and we discuss the implications of
the possible existence of a non-standard torus in M87 for the GeV to
TeV gamma-ray emission from the jet. In the case of the quasar 3C 273,
the disk emission is more important, we investigate to what extent
the size and location of the gamma-ray emitting blob exposed to the
anisotropic radiation field of the accretion disk affects the angular
dependence of the gamma-ray absorption.
Title: Variations of the magnetic fields in large solar flares
Authors: Schunker, H.; Donea, A. -C.
Bibcode: 2003SSRv..107...99S
Altcode:
We present preliminary results from high resolution observations
obtained with the Michelson Doppler Imager (MDI) instrument on
the SOHO of two large solar flares of 14 July 2000 and 24 November
2000. We show that rapid variations of the line-of-sight magnetic
field occured on a time scale of a few minutes during the flare
explosions. The reversibility/irreversibility of the magnetic field
of both active regions is a very good tool for understanding how
the magnetic energy is released in these flares. The observed sharp
increase of the magnetic energy density at the time of maximum of
the solar flare could involve an unknown component which deposited
supplementary energy into the system.
Title: Small-Angle Scattering and Diffusion: Application to
Relativistic Shock Acceleration
Authors: Protheroe, R. J.; Meli, A.; Donea, A. -C.
Bibcode: 2003SSRv..107..369P
Altcode: 2002astro.ph.10011P
We investigate ways of accurately simulating the propagation of
energetic charged particles over small times where the standard Monte
Carlo approximation to diffusive transport breaks down. We find that a
small-angle scattering procedure with appropriately chosen step-lengths
and scattering angles gives accurate results, and we apply this to the
simulation of propagation upstream in relativistic shock acceleration.
Title: How relevant is the torus activity/geometry for the TeV
gamma-rays emitted in the jets of M87?
Authors: Donea, A. -C.; Protheroe, R. J.
Bibcode: 2003ASPC..290..197D
Altcode: 2003agnc.conf..197D; 2003astro.ph..1433D
Motivated by unification schemes of active galactic nuclei, we review
evidence for the existence of small-scale dust tori and BLR in BL
Lacs and Fanaroff-Riley Class I radio galaxies. Since there is no
direct evidence of any thermal emission from tori the task we search
for indirect evidence (at any wavelength) for dust structures in the
centres of host galaxies. We propose that an existing jet-accretion
disk symbiosis can be extrapolated to provide a large scale-symbiosis
between other important dusty constituents of the blazar/FR-I family. In
the context of this symbiosis we discuss the interactions of GeV
and TeV gamma-rays produced in the jet with the infrared radiation
fields external to the jet in quasars and blazars, taking account
the anisotropy of the radiation. We also review what kind of torus
geometry would fit observations of quasars and blazars made at different
wavelengths best.
Title: A Hadronic Model for Gamma-Ray Loud Quasars
Authors: Donea, Alina C.; Protheroe, Raymond J.
Bibcode: 2003IAUJD..18E..35D
Altcode:
We model the spectral energy distribution of quasars with a model in
which the emission region in the jet contains a population of energetic
protons interacting with the ambient radiation fields originating both
inside and outside of the jet. The external target photon fields include
the accretion disk soft x-ray excess broad-line region and torus. The
high energy part of the spectral energy distribution results from a
cascade initiated by electrons from charged pion decay and gamma-rays
from neutron pion decay and involves synchrotron radiation inverse
compton scattering and photon-photon pair production. We apply this
model to some gamma-ray loud quasars.
Title: Absorption of GEV and Tev Gamma-Rays in Famous AGN
Authors: Donea, Alina
Bibcode: 2003IAUJD..18E..34D
Altcode:
M87 and 3C273 are famous AGN with powerful jets. High energy gamma-ray
emission from these jets has been calculated (Protheroe Reimer
Donea 2002; Protheroe Donea 2003) with hadronic models in which
accelerated protons interact with internal radiation (synchrotron)
and/or external radiation fields. Leptonic models have also been used to
model the gamma-ray emission of both objects (e.g. Bai Lee 2000). GeV
to TeV gamma-rays produced in the jets may or may not be absorbed by
photon-photon pair production in the radiation fields of the accretion
disk broad line region and torus. We investigate this problem for M87
and 3C 273. In the case of M87 a mis-alligned BL Lac object there
appears to be a deficiency in dust at parsec scales and we discuss
the implications of the possible existence of a non-standard torus in
M87 for the GeV to TeV gamma-ray emission from the jet. In the case of
the quasar 3C 273 the disk emission is more important we investigate
to what extent the size and location of the gamma-ray emitting blob
exposed to the anisotropic radiation field of the accretion disk
affects the angular dependence of the gamma-ray absorption
Title: Radiation fields of disk, BLR and torus in quasars and blazars:
implications for /γ-ray absorption
Authors: Donea, Alina-C.; Protheroe, R. J.
Bibcode: 2003APh....18..377D
Altcode: 2002astro.ph..2068D
The radiation fields external to the jets and originating from within
a few parsecs from the black hole, are discussed in this paper. They
are the direct radiation from an accretion disk in symbiosis with jets,
the radiation field from the broad line region (BLR) surrounding the
accretion disk, and the infrared radiation from a dusty torus. The
jet/disk symbiosis modifies the energetics in the central parsec of
active galactic nuclei (AGN) such that for a given accretion rate,
a powerful jet would occur at the expense of the disk luminosity, and
consequently the disk would less efficiently ionize the BLR clouds or
heat the dust in the torus, thereby affecting potentially important
target photon fields for interactions of /γ-rays, accelerated
electrons and protons along the jet. Motivated by unification
schemes of AGN, we briefly review the evidence for the existence of
BLRs and small-scale dust tori in BL Lacs and Fanaroff-Riley Class I
(FR-I) radio galaxies. We propose that an existing jet-accretion disk
symbiosis can be extrapolated to provide a large-scale symbiosis between
other important dusty constituents of the blazar/FR-I family. In the
present paper, we discuss in the context of this symbiosis interactions
of GeV and TeV /γ-rays produced in the jet with the various radiation
fields external to the jet in quasars and blazars, taking account the
anisotropy of the radiation.
Title: Gamma Ray and Infrared Emission from the M87 Jet and Torus
Authors: Donea, A. C.; Protheroe, R. J.
Bibcode: 2003PThPS.151..186D
Altcode: 2003astro.ph..3522D
The existence of intrinsic obscuration of Fanaroff-Riley I objects is a
controversial topic. M87, the nearest such object, is puzzling in that
although it has very massive central black hole it has a relatively
low luminosity, suggesting it is in a dormant state. Despite of its
proximity to us (16 Mpc) it is not known with certainty whether or not
M87 has a dusty torus. Infrared observations indicate that if a torus
exists in M87 it must have a rather low infrared luminosity. Using
arguments from unification theory of active galactic nuclei, we have
earlier suggested that the inner parsec-scale region of M87 could
still harbour a small torus sufficiently cold such that its infrared
emission is dwarfed by the jet emission. The infrared emission from even
a small cold torus could affect through photon-photon pair production
interactions the escape of 100 GeV to TeV energy gamma rays from the
central parsec of M87. /par The TeV gamma-ray flux from the inner jet
of M87 has recently been predicted in the context of the Synchrotron
Proton Blazar (SPB) model to extend up to at least 100~GeV (Protheroe,
Donea, Reimer, 2002). Subsequently, the detection of gamma-rays above
730 GeV by the HEGRA Cherenkov telescopes has been reported. We discuss
the interactions of gamma-rays produced in the inner jet of M87 with
the weak infrared radiation expected from a possible dusty small-scale
torus, and show that the HEGRA detection shows that the temperature of
any torus surrounding the gamma-ray emission region must be cooler than
about 250~K. We suggest that if no gamma-rays are in future detected
during extreme flaring activity in M87 at other wavelength, this may
be expected because of torus heating.
Title: Radiation Fields in Blazars - a Possible Extension of the Small
Scale Symbiosis (Disk/Jet) into a Large Scale (Dust/Dust) Symbiosis
Authors: Donea, Alina-C.; Protheroe, Raymond J.
Bibcode: 2002PASA...19...39D
Altcode:
In blazar models both protons and electrons may be efficiently
accelerated in jets and produce γ-rays. Here we discuss the
interactions of these γ-rays with different radiation fields. The
external radiation fields within a few parsecs from the black hole
involved in such interactions could be the direct radiation from the
accretion disk coupled with the jet, the infrared radiation from a
dusty torus, and the emission line radiation from the broad line region
surrounding the accretion disk. The optical thickness for absorption
of γ-ray photons in the external radiation fields is analysed for
blazars and quasars. Based on the unification theory of active galactic
nuclei we briefly review the evidence for the existence of small scale
dust tori in blazars/FR I. We propose that the existing jet-accretion
disk symbiosis extrapolates to a large scale symbiosis between other
important dusty constituents of the blazar/FR I family.
Title: The Structure of Accretion Flow at the Base of Jets in AGN
Authors: Donea, Alina-C.; Biermann, Peter L.
Bibcode: 2002PASA...19..125D
Altcode:
This paper discusses the boundary layer and the emission spectrum from
an accretion disk having a jet anchored at its inner radius, close
to the black hole. We summarise our earlier work and apply it to the
accretion disks of some blazars. We suggest that the `accretion disk
with jet' (ADJ) model could make the bridge between standard accretion
disk models (suitable for quasars and FRII sources) and low-power
advection dominated accretion disk models (suitable for some of the
low-power BL Lacs and FRI sources). The jet is collimated within a
very narrow region close to the black hole (nozzle). In our model it
is assumed that the boundary layer of the disk is the region between
radius Rms - the last marginally stable circular orbit
calculated for a Kerr geometry - and the radius Rjet, which
gives the thickness of the `footring', i.e. the base of the jet. We
analyse the size of the boundary layer of the disk where the jet is
fed with energy, mass, and angular momentum. As a consequence of the
angular momentum extraction, the accretion disk beyond Rjet
no longer has a Keplerian flow. A hot corona usually surrounds the disk,
and entrainment of the corona along the flow could also be important for
the energy and mass budget of the jet. We assume that the gravitational
energy available at the footring of the jet goes into the jet, and so
the spectrum from the accretion disk gives a total luminosity smaller
than that of a `standard' accretion disk, and our ADJ model should
apply for blazars with low central luminosities. Variations of the
boundary layer and nozzle may account for some of the variability
observed in active galactic nuclei.
Title: Complex electron energy distributions in supernova remnants
with non-thermal X-Rays
Authors: Donea, A. -C.; Biermann, P. L.; Protheroe, R. J.
Bibcode: 2001ICRC....5.1795D
Altcode: 2001ICRC...27.1795D
We address the problem of the diffusive acceleration of electrons
in shocks of supernova remnants with nonthermal X-ray emission. A
complex electron energy distribution develops, with energies within
the range of thermal to highly relativistic energies. Starting from
a Maxwellian distribution, drift acceleration produces, within the
finite-size layer of the shock, a steep power-law supra-thermal electron
energy distribution. Diffusive shock acceleration then produces an ∼
E-2.42±0.04 spectrum (Biermann, 1993). We find that at higher energies
the spectrum steepens, due to the existence of the individual blob
shocks and the substructure of the shock region (observed in radio
emission). We discuss the consequences of this for X-ray emission
in SNRs showing non-thermal emission. This may be a paradigm for
acceleration of energetic electrons also in other astrophysical sites,
such as clusters of galaxies.
Title: Tori and TeV gamma-ray emission in AGN
Authors: Donea, A. -C.; Protheroe, R. J.
Bibcode: 2001ICRC....7.2717D
Altcode: 2001ICRC...27.2717D
The absorption of TeV gamma-rays in active galactic nuclei by
photon-photon pair production on infrared radiation from a parsec scale
torus at temperature ∼ 1000 K surrounding the accretion disk/base
of jet was discussed by Protheroe and Biermann (Astropart. Phys., 6,
293, 1997). Here we briefly review the evidence for the existence of
dusty infrared tori in blazars, and construct torus models consistent
with infrared and optical polarimetry data. This leads us to propose
a symbiosis between large and small-scale dust features and broad
line regions in AGN. We discuss the radiation fields of the accretion
disk, broad line region and dusty torus as target photons for pion
photoproduction by protons and photon-photon pair production by
γ-rays. We use our results to constrain the sites of emission of TeV
gamma rays.
Title: The origin of the jet and the implication of the existing
disk-jet symbiosis for the γ-ray emission in AGN
Authors: Donea, Alina-C.; Masnou, Jean-Louis; Donea, Fănel
Bibcode: 2001AIPC..558..708D
Altcode: 2001hegr.proc..708D
Studying the symbiosis between the accretion disk, the bipolar outflows
and the supermassive black hole from the center of an active galactic
nucleus, one can infer the size of the base of the jet. The jet is
anchored at the boundary layer of the accretion disk extracting mass,
energy and angular momentum from the innermost region of the disk. This
has dramatic effects on the emission processes from the disk: the
UV spectrum from the disk driving the jet is cut at higher photon
energies. That means, the energy density of the UV photons from a
disk with jet is much smaller. The equations of the mass and energy
conservation are properly analyzed in the context of the existing
symbiosis in AGN. Since there are models explaining the TeV γ-ray
emission from blazars and quasar, as UV photons upscattered via the
inverse Compton effect by very high energy electrons, we address the
problem of the external Compton scattering mechanism for different
AGN. .
Title: Stochastic Seismic Emission from Acoustic Glories and the
Quiet Sun
Authors: Donea, A. -C.; Lindsey, C.; Braun, D. C.
Bibcode: 2000SoPh..192..321D
Altcode:
Helioseismic images of multipolar active regions show enhanced seismic
emission in 5-mHz oscillations in a halo surrounding the active region
called the `acoustic glory'. The acoustic glories contain elements
that sustain an average seismic emission 50% greater than similar
elements in the quiet Sun. The most intense seismic emitters tend to
form strings in non-magnetic regions, sometimes marking the borders of
weak magnetic regions and the separation between weak magnetic regions
of opposite polarity. This study compares the temporal character
of seismic emission from acoustic glories with that from the quiet
Sun. The power distribution of quiet-Sun seismic emission far from solar
activity is exponential, as for random Gaussian noise, and therefore
not perceivably episodic. The distribution of seismic power emanating
from the most intense elements that comprise the acoustic glories is
exponential out to approximately 4 times the average power emitted
by the quiet Sun. Above this threshold the latter distribution shows
significant saturation, suggesting the operation of a hydromechanical
non-linearity that sets limits on the acoustic power generated by
the convection zone. This could give us considerable insight into the
physical mechanism of seismic emission from the near subphotosphere.
Title: Solar Activity Level on the Ascending Phase of the Solar
Cycle 23
Authors: Maris, G.; Popescu, M. -D.; Oncica, A.; Donea, A. -C.
Bibcode: 2000ESASP.463..371M
Altcode: 2000sctc.proc..371M
No abstract at ADS
Title: Physics of the Base of the Outflow Jet in Active Galactic
Nuclei
Authors: Donea, Fanel; Donea, Alina-Catalina
Bibcode: 2000RoAJ...10..129D
Altcode: 2000RoAJ...10..131D
A new aspect of the physics of the base of the outflow jet at the
center of an active galactic nucleus is addressed. The energy budget,
including the conservation laws of mass are analysed in the context
of the existence of a self-symbiotic system with a black hole, a
relativistic disc and a bipolar outflow. The velocity of expansion
of the jet anchored at the boundary layer is analysed. A thorough
discussion is dedicated to the boundary layer and the corona of the
accretion disc.
Title: Bremsstrahlung emission from a complex distribution of
electrons
Authors: Donea, Alina-Catalina; Maris, Georgeta
Bibcode: 2000RoAJ...10...17D
Altcode:
The spacecraft observations in the heliosphere have proven that shocks
can accelerate particles with high efficiency, out of the superthermal
range of energies. Energetic particles exist everywhere in the universe
and shocks are commonly associated with them. We pay attention to
the model of diffusive shock acceleration for electrons. We compute
the continuum bremsstrahlung emission of a complex distribution of
electrons from thermal to highest energies.
Title: Disks with Jet, ADAF or EDAF for SGR A*
Authors: Donea, A. C.; Falcke, H.; Biermann, P. L.
Bibcode: 1999ASPC..186..162D
Altcode: 1999cpg..conf..162D; 1999astro.ph..9442D
We investigate various models of accretion disks for Sgr A*, one of
the most puzzling sources in the Galaxy. The generic image we have
taken into account consists of a black hole, an accretion disk, and
a jet. Various accretion models are able to explain the low NIR flux
of Sgr A*: a standard accretion disk with a jet, an ADAF, or an EDAF
(Ejection Dominated Accretion Flow) model. We find that all of these
models are conceptually similar. The accretion model which allows
the formation of the jet at the innermost edge of the disk requires a
sub-keplerian gas motion and a very large base of the jet. The large
base of the jet may be unrealistic for Sgr A*, since the jet model
and the observations suggest that the jet is collimated and anchored
in the disk in a very narrow region of the disk close to the black
hole. Alternatively, one can think of a jet plus wind model (EDAF),
where most of the energy goes out without being dissipated in the
disk. The model resembles the ADAF model at small radii. At large
radii the energy is ejected by a wind.
Title: Seismic Images of a Solar Flare
Authors: Donea, A. -C.; Braun, D. C.; Lindsey, C.
Bibcode: 1999ApJ...513L.143D
Altcode:
We have used helioseismic holography to render seismic images of
the solar flare of 1996 July 9, whose helioseismic signature was
recently reported by Kosovichev & Zharkova. We computed time
series of ``egression power maps'' in 2 mHz bands centered at 3.5 and
6 mHz. These images suggest an oblong acoustic source associated with
the flare some 18 Mm in the north-south direction and approximately 15
Mm in the east-west direction. The considerable preponderance of the
flare acoustic power emanates in the 3.5 mHz band. However, because
the ambient noise in the 6 mHz band is much lower and the diffraction
limit for 6 mHz waves is much finer, the flare is rendered far more
clearly in the 6 mHz band. The 6 mHz flare signature lags the 3.5 mHz
by approximately 4 minutes.
Title: Influence of the Outflow Jet on the Accretion Disk Structure
in AGN
Authors: Donea, Alina-Catalina
Bibcode: 1999RoAJ....9..115D
Altcode:
It is widely accepted that the center of an active galactic nucleus has
a supermassive black hole surrounded by an accretion disk. The radio
emissions reveal the existence of the outflows, which are believed to
originate from the innermost region of the disk. The most recent optical
and radio observations of AGN and the discovery of the quasi-periodic
oscillations in X-ray binaries reveal the importance of searching
the inner edge of the accretion disk assumed to be essential for
the formation of the jet in any kind of AGN. Based on the assumption
that the jet, the disk and the black hole are symbiotic elements of
a stable active system, we analyze the characteristic radii of the
disk with jet. The loss of mass and angular momentum through the jet
channel implies a recalculation of the structure of the disk, where
the opacity and pressure change.
Title: Seismic Images of a Solar Flare
Authors: Donea, Alina-C.; Braun, Doug C.; Lindsey, Charles A.
Bibcode: 1999soho....9E..13D
Altcode:
Helioseismic holography has given us remarkable images of the solar
flare of 1996 July 9. We computed time series of "egression power"
images in 2 mHz bands centered at 3.5 mHz and 6 mHz. These images show
an acoustic source associated with the flare some 18 Mm in the N-S
direction and approximately 15 Mm in the E-W. The flare is rendered
considerably more clearly in the 6 mHz band. The 6 mHz flare signature
lags the 3.5 mHz by approximately 4 min. The results offer a highly
encouraging assessment of the general diagnostic utility of seismic
holography for understanding the physics of solar flares.
Title: Stochastic Seismic Emission from Acoustic Glories and the
Quiet Sun
Authors: Donea, Alina-C.; Lindsey, Charles A.; Braun, Doug C.
Bibcode: 1999soho....9E..52D
Altcode:
Helioseismic images of multipolar active regions show enhanced seismic
emission in 5 mHz oscillations in a halo surrounding the active region
called the "acoustic glory." The acoustic glories contain seismic
elements that sustain an average seismic emission 50% greater than a
similar element of the quiet Sun. The most intense seismic emitters
tend to form strings in non-magnetic regions, sometimes marking the
borders of weak magnetic regions and even the separation between weak
magnetic regions of opposite polarity. This study compares the temporal
character of seismic emission from acoustic glories with that from the
quiet Sun. The distribution of quiet-Sun seismic power far from solar
activity is exponential, as for random Gaussian noise. The distribution
of seismic power emanating from the most intense elements that comprise
the acoustic glories is likewise exponential out to approximately 6
times the average power emitted by the quiet Sun. Above this threshold
the latter distribution shows significant saturation, suggesting the
operation of a hydromechanical non-linearity that sets limits on the
acoustic power generated by the convection zone. This could give us
considerable insight into the physical mechanism of seismic emission
from the near subphotosphere.
Title: Seismic images of the solar flare of July 9, 1996.
Authors: Donea, A. -C.; Braun, D. C.; Lindsey, C.
Bibcode: 1999joso.proc..124D
Altcode:
The helioseismic holography is a new method useful for rendering
seismic images of the solar flare of July 9, 1996. Time series of the
"egression power map" are computed in 2 mHz bands centered at 3.5
mHz and 6 mHz. The images show an acoustic source associated with the
flare some 18 mm in the N-S direction and approximately 15 mm in the
E-W. The flare is rendered far more clearly in the 6 mHz band. The 6
mHz flare signature lags the 3.5 mHz by approximately 6 minutes.
Title: Suprathermal electron acceleration in solar flares.
Authors: Donea, A. -C.; Maris, G.; Moise, E.
Bibcode: 1999joso.proc..176D
Altcode:
The non-Maxwellian electrons fill the gap in phase space, between the
thermal Maxwellian electrons and the solar cosmic ray electrons. The
thermal pool is provided by the immense mass of the hot solar
corona. Having an efficient injection mechanism the nonthermal
population of the electrons has to bridge between the thermal and solar
cosmic ray electrons. The authors investigated the acceleration of
suprathermal electrons and the way they modify the ionization balance
in the solar corona. The steep electron spectrum could explain the
steep X-ray fluxes measured during the solar flares.
Title: Helioseismic Holography - a Technique for Understanding
Solar Flares
Authors: Donea, A. C.; Lindsey, C.; Braun, D.
Bibcode: 1999RoAJ....9S..71D
Altcode:
The helioseismic holography is a technique which allows the analysis of
the photosphere of the Sun from the point of view of the acoustics. In
this paper we shall discuss mainly the seismic image of the flare of
July 9, 1996 which produced the largest sunquake observed by MDI-SOHO
instrument. We emphasize the fact that the kernel-like structure
observed in the seismic signature at both 3.5 mHz and 6 mHz egression
power maps are not side lobes effect. The seismic signature reveals
the presence of an extended acoustic source, much larger than the
Doppler redshift motion observed in the MDI-SOHO Dopplergrams.
Title: What can be inferred from the UV Continuum Emission from
Accretion Disks Driving Jets?
Authors: Donea, A. C.; Biermann, P. L.
Bibcode: 1998tma..conf..353D
Altcode:
No abstract at ADS
Title: Exploration of the Physical Consequences of the Jet-Disk
Symbiosis
Authors: Donea, A. C.; Biermann, P. L.
Bibcode: 1997rja..proc..122D
Altcode:
The UV continuum in quasars is assumed to originate from an accretion
disk surrounding a massive black hole. We explain the UV fluxes by
a theoretical model of a thin disk giving rise to a jet at the inner
boundaries close to the black hole. A first way in analyzing the jets is
to start looking at the boundary layer of the accretion disk. There the
jets take out energy, angular momentum and mass from the disk. We show
the strong symbiosis between the rotating black hole, the accretion
disk and the jet. We discuss the structure and emission spectrum of
a disk which drives a powerful jet. Due to the large efficiency of
extracting energy from the accreting matter in the inner part of the
disk close to the massive object, all the energetic conditions for
the formation of jets are fulfilled. The total energy going up into
the jet depends strongly on the Kerr black hole parameters, on the
disk features and on the mass flow and thickness of the jet.
Title: The symbiotic system in quasars: black hole, accretion disk
and jet.
Authors: Donea, A. -C.; Biermann, P. L.
Bibcode: 1996A&A...316...43D
Altcode: 1996astro.ph..2092D
The UV continuum spectrum of quasars and AGN is assumed to originate
from an accreting disk surrounding a massive rotating black hole. We
discuss the structure and emission spectra of a disk which drives a
powerful jet. Due to the large efficiency of extracting energy from the
accreting matter in the inner part of the disk close to the massive
object, all the energetic conditions for the formation of jets are
fulfilled. The total energy going up into the jet depends strongly on
the Kerr black hole parameters, on the disk features and on the mass
flow and thickness of the jet. The shape of UV spectra of the AGN can
be explained by a sub-Eddington accretion disk which drives a jet in
the innermost parts.
Title: Numerical Exploration of Lense-Thirring Precession Influence
on Artificial Satellite Motion
Authors: Stavinschi, M.; Mioc, V.; Donea, A.
Bibcode: 1996pacm.conf..377S
Altcode:
No abstract at ADS
Title: Analysis of the Long Period Terms of Local and Global Data
of UT1-AT
Authors: Stavinschi, Magdalena; Souchay, Jean; Donea, Alina-Catalina
Bibcode: 1994RoAJ....4...49S
Altcode:
In our analysis of UTO and UTI, the long period terms 18.6y,
13.9y, 12.5y, 11.1y, 9.2y have been emphasized. To be sure that the
results are trustworthy, different methods (Scargle for data unevenly
distributed,the classical least square method and Fourier analysis) have
been used for the data recorded as well at the Bucharest Observatory
and the data of IERS.
Title: About Long-Periodic Components of UT1 from Local Observations
Authors: Stavinschi, M.; Souchay, J.; Donea, A. C.
Bibcode: 1994dana.conf..423S
Altcode:
No abstract at ADS
Title: The Global Analysis of Time Determinations Made in Bucharest
During 1962-1989 (II)
Authors: Stavinschi, Magda; Dinescu, Dana; Vass, Gheorghi; Donea, Alina
Bibcode: 1993RoAJ....3...45S
Altcode:
The first part of this work was presented during the 7th International
Symposium of Geodesy and Geophysics of the Earth - - the IAG No. 122
Symposium - in Potsdam and was published in the Proceedings of the
Symposium (Springer Verlag, in print). Because at the moment of the
Symposium we only had preliminary results of the analysis, in the
present paper a complete image of the data processing and of the
results has been included.
Title: Effects of the Pole Movement on Time Determinations
Authors: Stavinschi, Magda; Dinescu, Dana; Vass, Gheorghe; Donea, Alina
Bibcode: 1993RoAJ....3..127S
Altcode:
Between 1957 and 1990, observations were made in Bucharest with a
passage instrument, in order to measure the non-uniformities in the
Earth's rotation. We set out to analyse the way in which longitude
variations may affect the periodicities indicated by the raw UTO -
AT observations (Rom. Astron. J., Vol. 3, No. 1, 1993).