arXiv subjects

E. F. Ivanov

Publications and source records attributed to E. F. Ivanov.

5 recordsLinked to original sources

arXiv2026

Electron Acceleration and Plasma Heating in an Impulsive Confined C-class Solar Flare

A detailed analysis of the impulsive C2.8 solar flare SOL2023-03-19T02:12 is presented, focusing on the microwave (MW) and X-ray domains. The flare was selected because of its impulsive nature, the relatively simple magnetic morphology of its parent active region (AR) NOAA 13256, its confined evolution, its moderate intensity, pronounced non-stationary temporal behaviour, and the availability of a unique multi-wavelength dataset. This dataset includes MW spectral observations in the frequency range 2.8-12 GHz obtained with the new Solar Radio Spectropolarimeter (SOLARSPEL), together with MW images from the Siberian Radioheliograph (SRH). The flare was also observed by two imaging X-ray telescopes, Solar Orbiter/STIX and ASO-S/HXI. Nonlinear force-free field extrapolations are used to reconstruct the three-dimensional magnetic configuration of the AR. We present evidence for a direct coupling between the thermal plasma and the non-thermal electron population in the frame of collisionless plasma during the initial flare stage. Some simple relationships about electron acceleration process are presented and discussed. Analysis of the extrapolated magnetic field indicates that the flare onset was associated with a system of low-lying sheared magnetic loops located along the polarity inversion line (PIL). Given the confined nature of the event and the reconstructed magnetic configuration, we infer that magnetic reconnection most likely occurred within current sheets possessing a substantial guide-field component. The observed non-stationary QPPs in the non-thermal emission, with periods decreasing from approximately 15 to 9 s, are interpreted as signatures of a sequence of magnetic reconnection episodes occurring in different magnetic structures and triggered quasi-periodically by a process that remains uncertain, but which may involve propagating slow magnetoacoustic waves.

astro-ph.SR↗

arXiv2018

Multi-instrument view on solar eruptive events observed with the Siberian Radioheliograph: From detection of small jets up to development of a shock wave and CME

The first 48-antenna stage of the Siberian Radioheliograph (SRH) started single-frequency test observations early in 2016, and since August 2016 it routinely observes the Sun at several frequencies in the 4-8 GHz range with an angular resolution of 1-2 arc minutes and an imaging interval of about 12 seconds. With limited opportunities of the incomplete antenna configuration, a high sensitivity of about 100 Jy allows the SRH to contribute to the studies of eruptive phenomena along three lines. First, some eruptions are directly visible in SRH images. Second, some small eruptions are detectable even without a detailed imaging information from microwave depressions caused by screening the background emission by cool erupted plasma. Third, SRH observations reveal new aspects of some events to be studied with different instruments. We focus on an eruptive C2.2 flare on 16 March 2016 around 06:40, one of the first flares observed by the SRH. Proceeding from SRH observations, we analyze this event using extreme-ultraviolet, hard X-ray, white-light, and metric radio data. An eruptive prominence expanded, brightened, and twisted, which indicates a time-extended process of the flux-rope formation together with the development of a large coronal mass ejection (CME). The observations rule out a passive role of the prominence in the CME formation. The abrupt prominence eruption impulsively excited a blast-wave-like shock, which appeared during the microwave burst and was manifested in an "EUV wave" and Type II radio burst. The shock wave decayed and did not transform into a bow shock because of the low speed of the CME. Nevertheless, this event produced a clear proton enhancement near Earth. Comparison with our previous studies of several events confirms that the impulsive-piston shock-excitation scenario is typical of various events.

astro-ph.SR↗

arXiv2017

Siberian Radioheliograph: First Results

Regular observations of active processes in the solar atmosphere have been started using the first stage of the multiwave Siberian Radioheliograph (SRH), a T-shaped 48-antenna array with a 4-8 GHz operating frequency range and a 10 MHz instantaneous receiving band. Antennas are mounted on the central antenna posts of the Siberian Solar Radio Telescope. The maximum baseline is 107.4 m, and the angular resolution is up to 70". We present examples of observations of the solar disk at different frequencies, "negative" bursts, and solar flares. The sensitivity to compact sources reaches 0.01 solar flux units ($\approx 10^{-4}$ of the total solar flux) with an accumulation time of about 0.3 s. The high sensitivity of SRH enables monitoring of solar activity and allows studying active processes from characteristics of their microwave emission, including faint events, which could not be detected previously.

astro-ph.SR↗

arXiv2014

96-antenna radioheliograph

Here we briefly present some design approaches for a multifrequency 96-antenna radioheliograph. The array antenna configuration, transmission lines and digital receivers are the main focus of this work. The radioheliograph is a T-shaped centrally-condensed radiointerferometer operating at the frequency range 4-8~GHz. The justification for the choice of such a configuration is discussed. The antenna signals are transmitted to a workroom by analog optical links. The dynamic range and phase errors of the microwave-over-optical signal are considered. The signals after downconverting are processed by the digital receivers for delay tracking and fringe stopping. The required delay tracking step and data rates are considered. Two 3-bit data streams (I and Q) are transmitted to a correlator with the transceivers embedded in FPGA (Field Programmed Gate Array) chips and with PCI Express cables.

astro-ph.IM↗

arXiv2012

The multifrequency Siberian Radioheliograph

The 10-antenna prototype of the multifrequency Siberian radioheliograph is described. The prototype consists of four parts: antennas with broadband front-ends, analog back-ends, digital receivers and a correlator. The prototype antennas are mounted on the outermost stations of the Siberian Solar Radio Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom by an analog fiber optical link, laid in an underground tunnel. After mixing, all signals are digitized and processed by digital receivers before the data are transmitted to the correlator. The digital receivers and the correlator are accessible by the LAN. The frequency range of the prototype is from 4 to 8 GHz. Currently the frequency switching observing mode is used. The prototype data include both circular polarizations at a number of frequencies given by a list. This prototype is the first stage of the multifrequency Siberian radioheliograph development. It is assumed that the radioheliograph will consist of 96 antennas and will occupy stations of the West-East-South subarray of the SSRT. The radioheliograph will be fully constructed in autumn of 2012. We plan to reach the brightness temperature sensitivity about 100 K for the snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and polarization measurement accuracy about a few percent. First results with the 10-antenna prototype are presented of observations of solar microwave bursts. The prototype abilities to estimate source size and locations at different frequencies are discussed.

astro-ph.IM↗