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The Late Gradual Phase of Large Flares: The Case of November 3, 2003  

Henry Aurass   Submitted: 2014-09-10 05:20

The hard X-ray time profiles of most solar eruptive events begin with an {it impulsive phase} which may be followed by a {it late gradual phase}. In a recent article (Aurass {it et al.} 2013, {it Astron. Astrophys.} {f 555}, A40) we analyzed the impulsive phase of the solar eruptive event on November 3, 2003 in radio and X-ray emission. We find evidence of magnetic breakout reconnection using the radio diagnostic of the common effect of the flare current sheet and, at heights of pm0.4Rs, of a coronal breakout current sheet (a source site that we call X). In this article we investigate the radio emission during the late gradual phase of the previously analyzed event. The work is based on 40-400~MHz dynamic spectra ({it Radio Spectrograph} Observatorium Tremsdorf, Leibniz Institut f''ur Astrophysik Potsdam, AIP) combined with radio images obtained by the French {it Nanc{c}ay Multifrequency Radio Heliograph} (NRH) of the Observatoire de Paris, Meudon. Additionally we use {it Ramaty High Energy Solar Spectroscopic Imager} (RHESSI) hard X-ray (HXR) flux records, and {it Solar and Heliospheric Observatory} (SOHO) {it Large Angle and Spectrometric Coronagraph} (LASCO) and {it Extreme ultraviolet Imaging Telescope} (EIT) images. The analysis shows that the late gradual phase is subdivided into two distinct stages. Stage 1 (here lasting five minutes) is restricted to reoccurring radio emission at source site X. We observe plasma emission and an azimuthally moving source (from X toward the NE; speed ab1200kms) at levels radially ordered {it against} the undisturbed coronal density gradient. These radio sources mark the lower boundary of an overdense region with a huge azimuthal extent. By the end of its motion, the source decays and reappears at point X. This is the onset of stage 2 traced here during its first 13~minutes. By this time, NRH sources observed at frequencies le236.6~MHz radially lift off with a speed of ab400kms (one third of the front speed of the coronal mass ejection (CME)) as one slowly decaying broadband source. This speed is still observable in SOHO/LASCO~C3 difference frames in the wake of the CME four hours later. In stage 2, the radio sources at higher frequencies appear directly above the active region with growing intensity. We interpret the observations as the transit of the lower boundary of the CME body through the height range of the coronal breakout current sheet. The relaxing global coronal field reconnects with the magnetic surroundings of the current sheets still connecting the CME in its wake with the Sun. The accelerated particles locally excite plasma emission but can escape also toward the active region, the CME, and the large-scale solar magnetic field. The breakout relaxation process may be a source of reconnection- and acceleration rate modulations. In this view, the late gradual phase is a certain stage of the coronal breakout relaxation after the release of the CME. This article is, to our best knowledge, the first observational report of the coronal breakout recovery. Our interpretation of the radio observations agrees with some predictions of magnetic breakout simulations ({it e.g.} Lynch {it et al.} 2008, {it Astrophys. Journ.} {f 683}, 1192). Again, combined spectral and imaging radio observations give a unique access to dynamic coronal processes which are invisible in other spectral ranges.

Authors: H. Aurass
Projects: GOES X-rays ,Nançay Radioheliograph,Other,RHESSI,SoHO-EIT,SoHO-MDI,SoHO-LASCO

Publication Status: Solar Physics 289, 12, 4517-4531 (2014). DOI 10.1007/s11207-014-0604-9
Last Modified: 2014-11-24 07:25
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The Late Gradual Phase of Large Flares: The Case of November 3, 2003  

Henry Aurass   Submitted: 2014-09-10 05:20

The hard X-ray time profiles of most solar eruptive events begin with an impulsive phase which may be followed by a late gradual phase. In a recent article (Aurass et al. 2013, Astron. Astrophys. {\bf 555}, A40) we analyzed the impulsive phase of the solar eruptive event on November 3, 2003 in radio and X-ray emission. We find evidence of magnetic breakout reconnection using the radio diagnostic of the common effect of the flare current sheet and, at heights of ±0.4\Rs, of a coronal breakout current sheet (a source site that we call X). In this article we investigate the radio emission during the late gradual phase of the previously analyzed event. The work is based on 40-400~MHz dynamic spectra ( Radio Spectrograph Observatorium Tremsdorf, Leibniz Institut f\"ur Astrophysik Potsdam, AIP) combined with radio images obtained by the French Nan\c{cay Multifrequency Radio Heliograph} (NRH) of the Observatoire de Paris, Meudon. Additionally we use Ramaty High Energy Solar Spectroscopic Imager (RHESSI) hard X-ray (HXR) flux records, and Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) and Extreme ultraviolet Imaging Telescope (EIT) images. The analysis shows that the late gradual phase is subdivided into two distinct stages. Stage 1 (here lasting five minutes) is restricted to reoccurring radio emission at source site X. We observe plasma emission and an azimuthally moving source (from X toward the NE; speed \ab1200\kms) at levels radially ordered against the undisturbed coronal density gradient. These radio sources mark the lower boundary of an overdense region with a huge azimuthal extent. By the end of its motion, the source decays and reappears at point X. This is the onset of stage 2 traced here during its first 13~minutes. By this time, NRH sources observed at frequencies ≤236.6~MHz radially lift off with a speed of \ab400\kms (one third of the front speed of the coronal mass ejection (CME)) as one slowly decaying broadband source. This speed is still observable in SOHO/LASCO~C3 difference frames in the wake of the CME four hours later. In stage 2, the radio sources at higher frequencies appear directly above the active region with growing intensity. We interpret the observations as the transit of the lower boundary of the CME body through the height range of the coronal breakout current sheet. The relaxing global coronal field reconnects with the magnetic surroundings of the current sheets still connecting the CME in its wake with the Sun. The accelerated particles locally excite plasma emission but can escape also toward the active region, the CME, and the large-scale solar magnetic field. The breakout relaxation process may be a source of reconnection- and acceleration rate modulations. In this view, the late gradual phase is a certain stage of the coronal breakout relaxation after the release of the CME. This article is, to our best knowledge, the first observational report of the coronal breakout recovery. Our interpretation of the radio observations agrees with some predictions of magnetic breakout simulations ( e.g. Lynch et al. 2008, Astrophys. Journ. {\bf 683}, 1192). Again, combined spectral and imaging radio observations give a unique access to dynamic coronal processes which are invisible in other spectral ranges.

Authors: H. Aurass
Projects: RHESSI

Publication Status: Solar Physics, accepted
Last Modified: 2014-09-10 08:11
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Radio evidence for breakout reconnection in solar eruptive events  

Henry Aurass   Submitted: 2013-05-30 03:26

Magnetic reconnection is understood to be fundamental to energy release in solar eruptive events (SEEs). In these events reconnection produces a magnetic flux rope above an arcade of hot flare loops. Breakout reconnection, a secondary reconnection high in the corona between this flux rope and the overlying magnetic field, has been hypothesized. Direct observational evidence for breakout reconnection has been elusive, however. The aim of this study is to establish a plausible interpretation of the combined radio and hard X-ray (HXR) emissions observed during the impulsive phase of the near-limb X3.9-class SEE on 2003 November 03. We study radio spectra (AIP), simultaneous radio images (Nanc{c}ay Multi-frequency Radio Heliograph, NRH), and single-frequency polarimeter data (OAT). The radio emission is nonthermal plasma radiation with a complex structure in frequency and time. Emphasis is on the time interval when the HXR flare loop height was observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to be at its minimum and an X-ray source was observed above the top of the arcade loops. Two stationary, meter-wavelength sources are observed radially aligned at 0.18 and 0.41Rs above the active region and hard X-ray sources. The lower source is apparently associated with the upper reconnection jet of the flare current sheet (CS), and the upper source is apparently associated with breakout reconnection. Sources observed at lower radio frequencies surround the upper source at the expected locations of the breakout reconnection jets. We believe the upper radio source is the most compelling evidence to date for the onset of breakout reconnection during a SEE. The height stationarity of the breakout sources and their dynamic radio spectrum discriminate them from propagating disturbances. Timing and location arguments reveal for the first time that both the earlier described ``above the flare loop top'' HXR source and the lower radio source are emission from the upper reconnection jet above the vertical flare CS.

Authors: H. Aurass, G. Holman, S. Braune, G. Mann, P. Zlobec
Projects:

Publication Status: Astronomy and Astrophysics 555, A40 (2013)
Last Modified: 2013-07-01 07:21
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Radio evidence of break-out reconnection?  

Henry Aurass   Submitted: 2011-01-24 02:00

We reconsider the Oct. 28, 2003 X17 flare/coronal mass ejection studying the five minutes immediately before the impulsive flare phase (not yet discussed in previous work). To this aim are composed: complementary dynamic radio spectrograms, single frequency polarimeter records, radio images, as well as space-based longitudinal field magnetograms and ultra-violet images. We find widely distributed faint and narrowband meter wave radio sources located outside of active regions but associated with the boundaries of magnetic flux connectivity cells, inferred from the potential extrapolation of the observed photospheric longitudinal field as a model for coronal magnetic field structures. The radio sources occured during the initial decimeter wave effects well-known to be associated with the filament destabilization in the flaring active region (here NOAA 10486). Antiochos et al. (1999, ApJ 510, 485) predict in their break-out model for CME initiation that '' ... huge phenomena ... may be controled by detailed plasma processes that occur in relatively tiny regions''. They suggest that the expected faint energy release '' ... on long field lines far away from any neutral line ... may be detectable in radio/microwave emission from non-thermal particles ...''. In this paper we describe meter wave sources whose properties correctly coincide with the quoted predictions of the break-out reconnection model of CME initiation.

Authors: H. Aurass, G. Mann, P. Zlobec, M. Karlický
Projects: None

Publication Status: ApJ accepted (Jan. 21, 2011)
Last Modified: 2011-01-25 07:31
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A microflare with hard X-ray-correlated gyroresonance line emission at 314~MHz  

Henry Aurass   Submitted: 2010-01-12 07:27

Small energy release events in the solar corona can give insights into the flare process which are regularly hidden in the complex morphology of larger events. For one case we find a narrowband radio signal well correlated with the hard X-ray flare. We investigate wether these signals are probes for the flare current sheet. We aim to establish the relation between narrowband and short-duration features (<1% of the observing frequency in the spectral range 250-340~MHz, and some 5s until 2min, respectively) in dynamic radio spectral diagrams and simultaneously occuring HXR bursts. We use dynamic radio spectra from the Astrophysical Institute Potsdam, HXR images of RHESSI, TRACE coronal and chromospheric images, SOHO-MDI high resolution magnetogram data, and its potential field extrapolation for the analysis of one small flare event in AR10465 on September 26, 2003. We point to similar effects in e.g. the X-class flare on November 03, 2003 to demonstrate that we are not dealing with a singular phenomenon. We confirm the solar origin of the extremely narrowband radio emission. From RHESSI images and the magnetic field data we identify the probable site of the radio source as well as the HXR footpoint and the SXR flare loop emission. The flare loop is included in an ongoing change of magnetic connectivity as confirmed by TRACE images of hot coronal loops. The flare energy is stored in the nonpotential magnetic field substructure around the microflare site which is relaxed to a potential one. We conclude that the correlated HXR footpoint/narrowband radio emission, and the transition to a second energy release in HXR without associated radio emission are direct probes of changing magnetic connectivity during the flare. We suppose that the narrowband radio emission is due to gyroresonance radiation at the second harmonic of the local electron cyclotron frequency. It follows an upper limit of the magnetic field in the radio source volume of less than 50% of the mean potential field in the same height range. This supports the idea that the narrowband radio source is situated in the immediate surroundings of the flare current sheet.

Authors: H. Aurass, G. Rausche, S. Berkebile-Stoiser, A. Veronig
Projects: RHESSI,SoHO-EIT,SoHO-MDI,TRACE

Publication Status: A & A (in press)
Last Modified: 2010-01-12 08:51
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Coronal current sheet signatures during the 17 May 2002 CME-flare  

Henry Aurass   Submitted: 2009-08-20 04:50

The relation between current sheets (CSs) associated with flares, revealed by characteristic radio signatures, and current sheets associated with Coronal Mass Ejections (CMEs), detected in coronal ultra-violet (UV) and white light data, has not been analyzed, yet. We aim at establishing the relationship between CSs associated with a limb flare and CSs associated with the CME which apparently develops after the flare, on the basis of a unique data set, acquired on May 17, 2002, which includes radio and extreme ultra-violet (XUV) observations. Spectral radio diagnostics as well as UV spectroscopic techniques together with white light coronograph imaging and (partly) radio imaging are used to illustrate the relation between the CSs and to infer the physical parameters of the radially aligned features that develop in the aftermath of the CME. During the flare, drifting pulsating structures in dynamic radio spectra, an erupting filament, expanding coronal loops morphologically reminding to the later white light CME and associated with earlier reported hard X-ray source sites, are interpreted in accordance with earlier work and with reference to the common eruptive flare scenario as evidence of flare CSs in the low corona. In the aftermath of the CME, UV spectra allowed us to give an estimate of the CS temperature and density, over the 1.5 - 2.1 Rs interval of heliocentric altitudes. The UV detected CS, however, appears to be only one of many current sheets that exist underneath the erupting flux rope. A type II burst following in time at lower frequencies the CME radio continuum is considered as radio signature of a coronal shock excited at the flank of the CME. The results show that we can build an overall scenario where the CME is interpreted in terms of an erupting arcade crossing the limb of the Sun and connected to underlying structures via multiple CSs. Eventually, the observed limb flare seems to be a consequence of the ongoing CME.

Authors: H. Aurass, F. Landini, G. Poletto
Projects: None

Publication Status: A & A accepted
Last Modified: 2009-08-20 07:55
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The GLE on Oct. 28, 2003 - radio diagnostics of relativistic electron and proton injection  

Henry Aurass   Submitted: 2006-08-31 03:00

Timing discrepancies between signatures of accelerated particles at the sun and the arrival times of the particles at near-earth detectors are a matter of fundamental interest for space-weather applications. The solar injection times of various components of energetic particles were derived by Klassen et al. (2005) for the October 28, 2003, X-class / gamma-ray flare in NOAA AR10486. This flare occured in connection with a fast halo coronal mass ejection and a neutron monitor-observed ground level event (GLE). We used radio (Astrophysikalisches Institut Potsdam, WIND, Nancay Multifrequency Radio Heliograph), Hα (Observatorium Kanzelhoehe), RHESSI, SOHO (EIT, LASCO, MDI), and TRACE data to study the associated chromospheric and low coronal phenomena. We identify three source sites of accelerated particles in this event. Firstly, there is a source in projection 0.3Rs away from AR10486, which is the site of the reconnection outflow termination, as revealed by a termination shock signature in the dynamic radio spectrum. Secondly, there is the extended current sheet above a giant coronal postflare loop system in the main flare phase. Thirdly, there is a source situated on a magnetic separatrix surface between several magnetic arcades and neighbouring active regions. This source is 0.2Rs away from AR10486 and acts during onset and growth of high energy proton injection in space. It is not clear if this source is related to the acceleration of protons, or if it only confirms that energetic particles penetrate a multistructure magnetic loop system after being previously accelerated near the main HXR- and gamma-ray sources. The result is in favour of energetic particle acceleration in the low corona (<0.5Rs above the photosphere) and in contrast to acceleration of the relativistic particles at remotely propagating shock waves.

Authors: H. Aurass, G. Mann, G. Rausche, and A. Warmuth
Projects: RHESSI,SoHO-EIT,SoHO-MDI,TRACE

Publication Status: A&A 2006 in press
Last Modified: 2006-08-31 10:17
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Abstracts by Author
The Late Gradual Phase of Large Flares: The Case of November 3, 2003
The Late Gradual Phase of Large Flares: The Case of November 3, 2003
Radio evidence for breakout reconnection in solar eruptive events
Radio evidence of break-out reconnection?
A microflare with hard X-ray-correlated gyroresonance line emission at 314~MHz
Coronal current sheet signatures during the 17 May 2002 CME-flare
The GLE on Oct. 28, 2003 - radio diagnostics of relativistic electron and proton injection

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