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Common origin of quasi-periodic pulsations in microwave and decimetric solar radio bursts  

Larisa Kashapova   Submitted: 2021-10-18 22:12

We analyse quasi-periodic pulsations (QPP) detected in the microwave and decimeter radio emission of the SOL2017-09-05T07:04 solar flare, using simultaneous observations by the Siberian Radioheliograph 48 (SRH-48, 4-8 GHz) and Mingantu Spectral Radioheliograph (MUSER-I, 0.4-2 GHz). The microwave emission was broadband with a typical gyrosynchrotron spectrum, while a quasi-periodic enhancement of the decimetric emission appeared in a narrow spectral band (500-700 MHz), consistent with the coherent plasma emission mechanism. The periodicity that we found in microwaves is about 30 s, coming from a compact loop-like source with a typical height of about 31 Mm. The decimetric emission demonstrated a periodicity about 6 s. We suggested a qualitative scenario linking the QPPs observed in both incoherent and coherent spectral bands and their generation mechanisms. The properties of the QPPs found in the microwave signal are typical for perturbations of the flare loop by the standing sausage mode of a fast magnetohydrodynamic (MHD) wave. Our analysis indicated that this sausage-oscillating flare loop was the primary source of oscillations in the discussed event. The suggested scenario is that a fundamental sausage harmonic is the dominant cause for the observed QPPs in the microwave emission. The initiation of oscillations in the decimetric emission is caused by the third sausage harmonic via periodic and nonlinear triggering of the acceleration processes in the current sheets, formed at the interface between the sausage-oscillating flare loop and the external coronal loop that extended to higher altitudes. Our results demonstrate the possible role of MHD wave processes in the release and transport of energy during solar flares, linking coherent and incoherent radio emission mechanisms.

Authors: Larisa Kashapova, Dmitrii Kolotkov, Elena Kupriyanova, Anastasiia Kudriavtseva, Chengming Tan, Hamish Reid
Projects: GOES X-rays,Other,PROBA2/SWAP

Publication Status: Accepted for publication to Solar Physics
Last Modified: 2021-10-20 13:07
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The morphology of average solar flare time profiles from observations of the Sun's lower atmosphere  

Larisa Kashapova   Submitted: 2021-04-24 03:14

We study the decay phase of solar flares in several spectral bands using a method based on that successfully applied to white light flares observed on an M4 dwarf. We selected and processed 102 events detected in the Sun-as-a-star flux obtained with SDO/AIA images in the 1600~ and 304~ channels and 54 events detected in the 1700~ channel. The main criterion for the selection of time profiles was a slow, continuous flux decay without significant new bursts. The obtained averaged time profiles were fitted with analytical templates, using different time intervals, that consisted of a combination of two independent exponents or a broken power law. The average flare profile observed in the 1700~ channel decayed more slowly than the average flare profile observed on the M4 dwarf. As the 1700~ emission is associated with a similar temperature to that usually ascribed to M dwarf flares, this implies that the M dwarf flare emission comes from a more dense layer than solar flare emission in the 1700~ band. The cooling processes in solar flares were best described by the two exponents model, fitted over the intervals t1=[0, 0.5]t1/2 and t2=[3, 10]t1/2 where t1/2 is time taken for the profile to decay to half the maximum value. The broken power law model provided a good fit to the first decay phase, as it was able to account for the impact of chromospheric plasma evaporation, but it did not successfully fit the second decay phase.

Authors: Larisa K. Kashapova, Anne-Marie Broomhall, Alena I. Larionova, Elena G. Kupriyanova, Ilya D. Motyk
Projects: SDO-AIA

Publication Status: Published in MNRAS
Last Modified: 2021-04-25 15:35
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Detection of acceleration processes during the initial phase of the 12 June 2010 flare  

Larisa Kashapova   Submitted: 2012-05-13 21:11

We present analysis of plasma parameters during the initial phase of the 12 June 2010 flare (SOL2010-06-12T00:57). Peculiarity of the flare was detection of gamma-emission that is unusual for the such weak and short event. The analysis revealed the flare precursor detected about 5 minute before the flare onset on 94 Å images which spatially coincided with Neutral Line associated Source (NLS) indicated by the non-polarized MW source at 17 GHz (NORH). A comparison of results obtained from microwave (MW) data by the Nobeyama Radio Polarimeter and the Siberian Solar Radio Telescope (the new 10-antenna radio heliograph prototype at 4.6 and 6.4 GHz) and hard X-ray (HXR) observations by the Fermi Gamma-ray Space Telescope reveal presence of accelerated electrons at the initial phase the flare development. The analysis of MW and HXR spectra also confirms presence of accelerated particles. Moreover a good temporal correlation between several lightcurves of HXR energy bands and MW frequencies indicates to generation of both HXR and MW emission by the common populations of accelerated electrons. Detection of accelerated particles during the initial phase of the flare and SHH (soft-hard-harder) behaviour of the spectra points to several episodes of particle acceleration and confirms the non-impulsive type of the flare evolution.

Authors: L.K. Kashapova, N.S.Meshalkina, M.S.Kisil
Projects: None

Publication Status: Solar Phys (accepted)
Last Modified: 2012-05-14 12:11
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Abstracts by Author
Common origin of quasi-periodic pulsations in microwave and decimetric solar radio bursts
The morphology of average solar flare time profiles from observations of the Sun's lower atmosphere
Detection of acceleration processes during the initial phase of the 12 June 2010 flare

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