The origin of quasi-periodicities during circular ribbon flares

Solar flares with a fan-spine magnetic topology can form circular ribbons. The previous study based on H\alpha line observations of the solar flares during March 05, 2014 by Xu et al. (2017) revealed uniform and continuous rotation of the magnetic fan-spine. Preliminary analysis of the flare time profiles revealed quasi-periodic pulsations (QPPs) with similar properties in hard X-rays, H\alpha, and microwaves. In this work, we address which process the observed periodicities are related to: periodic acceleration of electrons or plasma heating? QPPs are analysed in the H\alpha emission from the centre of the fan (inner ribbon R1), a circular ribbon (R2), a remote source (R3), and an elongated ribbon (R4) located between R2 and R3. The methods of correlation, Fourier, wavelet, and empirical mode decomposition are used. QPPs in H\alpha emission are compared with those in microwave and X-ray emission. We found multi-wavelength QPPs with periods around 150 s, 125 s, and 190 s. The 150-s period is seen to co-exist in H\alpha, hard X-rays, and microwave emissions, that allowed us to connect it with flare kernels R1 and R2. These kernels spatially coincide with the site of the primary flare energy release. The 125-s period is found in the H\alpha emission of the elongated ribbon R4 and the microwave emission at 5.7 GHz during the decay phase. The 190-s period is present in the emission during all flare phases in the H\alpha emission of both the remote source R3 and the elongated ribbon R4, in soft X-rays, and microwaves at 4--8 GHz. We connected the dominant 150-s QPPs with the slipping reconnection mechanism occurring in the fan. We suggested that the period of 125 s in the elongated ribbon can be caused by a kink oscillation of the outer spine connecting the primary reconnection site with the remote footpoint. The period of 190 s is associated with the 3-min sunspot oscillations.Comment: Accepted for publication in A&

Diagnostics of electron beam properties from the simultaneous hard X-ray and microwave emission in the 10 March 2001 flare

Simultaneous simulation of HXR and MW emission with the same populations of electrons is still a great challenge for interpretation of observations in real events. In this paper we apply the FP kinetic model of precipitation of electron beam with energy range from 12 keV to 1.2 MeV to the interpretation of X-ray and microwave emissions observed in the flare of 10 March 2001. Methods. The theoretical HXR and MW emissions were calculated by using the distribution functions of electron beams found by solving time-dependent Fokker-Planck approach in a converging magnetic field (Zharkova at al., 2010; Kuznetsov and Zharkova, 2010) for anisotropic scattering of beam electrons on the ambient particles in Coloumb collisions and Ohmic losses. The simultaneous observed HXR photon spectra and frequency distribution of MW emission and polarization were fit by those simulated from FP models which include the effects of electric field induced by beam electrons and precipitation into a converging magnetic loop. Magnetic field strengths in the footpoints on the photosphere were updated with newly calibrated SOHO/MDI data. The observed HXR energy spectrum above 10 keV is shown to be a double power law which was fit precisely by the photon HXR spectrum simulated for the model including the self-induced electric field but without magnetic convergence. The MW emission simulated for different models of electron precipitation revealed a better fit to the observed distribution at higher frequencies for the models combining collisions and electric field effects with a moderate magnetic field convergence of 2. The MW simulations were able to reproduce closely the main features of the MW emission observed at higher frequencies.Comment: 17 pages, 10 figures in press; A&A 201

Flare Source Localization of SOL2022-02-03t4:21UT Event Using Microwawe Observations by Siberian Radiogeliograph

В работе представлены результаты исследования солнечной вспышки, произошедшей 3 февраля 2022 г. в 04:21UT. Данное событие класса С1 по GOES и длительностью менее 100 с имело сложный временной профиль, состоящий из нескольких всплесков. Была проведена локализация источников всплесков, обнаруженных с помощью данных Сибирского радиогелиографа, на частоте 5.8 ГГц. Анализ разностей изображений Солнца, полученных до начала события и во время вспышки, показал, что все источники всплесков относились к одному событию и произошли в активной области NOAA 12936. Сделана оценка потока источников микроволнового излучения вспышки на частоте 5.8 ГГц, его значения не превышали 1 солнечную единицу потока (С. Е. П.).In the paper, we present the analysis results obtained for the solar flare occurred at 04:21UT on February 3, 2023. The C1 GOES class event with duration less 100 seconds had a complicated time profile consisting of several bursts. Location of burst sources, found in the microwave time profile of the flare, was obtained using data by the Siberian radiogeoliograph. Analysis of solar image differences obtained before the event and during the bursts showed that all sources were part of the same event and occurred in the active region NOAA 12936. Estimated flux of microwave emission sources at a frequency of 5.8 GHz was less than 1 sfu. Keywords: solar flares, flares, microwaves

KW-Sun: The Konus-Wind Solar Flare Database in Hard X-ray and Soft Gamma-ray Ranges

We present a database of solar flares registered by the Konus-Wind instrument during more than 27 years of operation, from 1994 November to now (2022 June). The constantly updated database (hereafter KW-Sun) contains over 1000 events detected in the instrument's triggered mode and is accessible online at http://www.ioffe.ru/LEA/kwsun/. For each flare, the database provides time-resolved energy spectra in energy range from ~20 keV to ~15 MeV in FITS format along with count rate light curves in three wide energy bands G1 (~20-80 keV), G2 (~80-300 keV), and G3 (~300-1200 keV) with high time resolution (down to 16 ms) in ASCII and IDL SAV formats. This article focuses on the instrument capabilities in the context of solar observations, the structure of the KW-Sun data and their intended usage. The presented homogeneous data set obtained in the broad energy range with high temporal resolution during more than two full solar cycles is beneficial for both statistical and case studies as well as a source of context data for solar flare research.Comment: 10 pages, 6 figures, 1 table. Accepted for publication in ApJ