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Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra  

Nataliia Meshalkina   Submitted: 2020-09-22 23:03

On 23 July 2016 after 05:00 UTC, the first 48-antenna stage of the Siberian Radioheliograph detected two flares, M7.6 and M5.5, which occurred within half an hour in the same active region. Their multi-instrument analysis reveals the following. The microwave spectra were flattened at low frequencies and the spectrum of the stronger burst had a lower turnover frequency. Each flare was eruptive, emitted hard X-rays and γ -rays exceeding 800 keV, and had a rare three-ribbon configuration. An extended hard X-ray source associated with a longest middle ribbon was observed in the second flare. Unusual properties of the microwave spectra are accounted for by a distributed multi-loop system in an asymmetric magnetic configuration that our modeling supports. Microwave images did not resolve compact configurations in these flares, which may also be revealed incompletely in hard Xray images because of their limited dynamic range. Being apparently simple and compact, non-thermal sources corresponded to the structures observed in the extreme ultraviolet. In the scenario proposed for two successive eruptive flares in a configuration with a coronal magnetic null, the first filament eruption causes a flare and facilitates the second eruption that also results in a flare. Three persistent flare ribbons reflect magnetic reconnection at the coronal-null region forced by the filament motions.

Authors: V.V. Grechnev, N.S. Meshalkina, A.M. Uralov, A.A. Kochanov, S.V. Lesovoi, I.I. Myshyakov, V.I. Kiselev, D.A. Zhdanov, A.T. Altyntsev, M.V. Globa
Projects: None

Publication Status: Accepted in Solar Physics
Last Modified: 2020-09-23 13:11
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Sources of Quasi-Periodic Pulses in the 18 August 2012 Flare  

Nataliia Meshalkina   Submitted: 2016-01-11 20:01

We analyzed spatial and spectral characteristics of quasi-periodic pulses (QPP) for the 18 August 2012 limb are, using new data from a complex of spectral and imaging instruments developed by the Siberian Solar Radio Telescope team and the Wind/Konus gamma-ray spectrometer. A sequence of broadband pulses with periods of approximately ten seconds were observed in X-rays at energies between 25 keV and 300 keV, and in microwaves at frequencies from a few GHz up to 34 GHz during an interval of one minute. The QPP X-ray source was located slightly above the limb where the south legs of large and small EUV loop systems were close to each other. Before the QPPs the soft X-ray emission and the Ramaty High Energy Solar Spectroscopic Imager signal from the energy channels below 25 keV were gradually arising for several minutes at the same location. It was found that each X-ray pulse showed the soft-hard-soft behavior. The 17 and 34 GHz microwave source were at footpoints of the small loop system and the source emitting in the 4.2 - 7.4 GHz band in the large one. The QPPs were probably generated by modulation of acceleration processes in the energy release site. Analyzing radio spectra we determined the plasma parameters in the radio sources. The microwave pulses could be explained by relatively weak variations of the spectrum hardness of emitting electrons.

Authors: A. Altyntsev, N. Meshalkina, H. Meszarosova, M. Karlický, V. Palshin, S. Lesovoi
Projects: None

Publication Status: Solar Physics, in press
Last Modified: 2016-01-13 12:41
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Spectral and spatial observations of microwave spikes and zebra structure in the short radio burst of May 29, 2003  

Nataliia Meshalkina   Submitted: 2011-11-23 22:30

The unusual radio burst of May 29, 2003 connected with the M1.5 flare in AR10368 has been analyzed. It was observed by the Solar Broadband RadioSpectrometer (SBRS/Huairou station, Beijing) in the 5.2-7.6 GHz range. Itproved to be only the third case of a neat zebra structure appearing among allobservations at such high frequencies. Despite the short duration of the burst(25 s), it provided a wealth of data for studying the superfine structure withmillisecond resolution (5 ms). We localize the site of emission sources in theflare region, estimate plasma parameters in the generation sites, and suggestapplicable mechanisms for interpretating spikes and zebra-structure generation.Positions of radio bursts were obtained by the Siberian Solar Radio Telescope(SSRT) (5.7 GHz) and Nobeyama radioheliograph (NoRH) (17 GHz). The sources inintensity gravitated to tops of short loops at 17 GHz, and to long loops at 5.7GHz. Short pulses at 17 GHz (with a temporal resolution of 100 ms) areregistered in the R-polarized source over the N-magnetic polarity(extraordinary mode). Dynamic spectra show that all the emission comprisedmillisecond pulses (spikes) of 5-10 ms duration in the instantaneous band of 70to 100 MHz, forming the superfine structure of different bursts, essentially inthe form of fast or slow-drift fibers and various zebra-structure stripes. Fivescales of zebra structures have been singled out. As the main mechanism forgenerating spikes (as the initial emission) we suggest the coalescence ofplasma waves with whistlers in the pulse regime of interaction betweenwhistlers and ion-sound waves. In this case one can explain the appearance offibers and sporadic zebra-structure stripes exhibiting the frequency splitting.

Authors: G. P. Chernov, R. A. Sych, N. S. Meshalkina, Y. Yan, and C. Tan
Projects: None

Publication Status: A&A in press
Last Modified: 2011-11-24 02:52
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Radioheliograph observations of microwave bursts with zebra structures  

Nataliia Meshalkina   Submitted: 2011-09-27 18:20

The so-called zebra structures in radio dynamic spectra, specifically theirfrequencies and frequency drifts of emission stripes, contain information onthe plasma parameters in the coronal part of flare loops. This paper presentsobservations of zebra structures in a microwave range. Dynamic spectra wererecorded by Chinese spectro-polarimeters in the frequency band close to theworking frequencies of the Siberian Solar Radio Telescope. The emission sourcesare localized in the flare regions, and we are able to estimate the plasmaparameters in the generation sites using X-ray data. The interpretation of thezebra structures in terms of the existing theories is discussed. The conclusionhas been arrived that the preferred generation mechanism of zebra structures inthe microwave range is the conversion of plasma waves to electromagneticemission on the double plasma resonance surfaces distributed across a flareloop.

Authors: A.T. Altyntsev, S.V. Lesovoi, N.S. Meshalkina, R.A. Sych, Y. Yan
Projects: None

Publication Status: 10.1007/s11207-011-9856-9
Last Modified: 2011-09-28 10:02
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Abstracts by Author
Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra
Sources of Quasi-Periodic Pulses in the 18 August 2012 Flare
Spectral and spatial observations of microwave spikes and zebra structure in the short radio burst of May 29, 2003
Radioheliograph observations of microwave bursts with zebra structures

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