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The 26 December 2001 Solar Eruptive Event Responsible for GLE63. II. Multi-Loop Structure of Microwave Sources in a Major Long-Duration flare  

Alexey Kochanov   Submitted: 2016-11-29 00:38

Analysis of the observations of the SOL2001-12-26 event related to ground-level-event GLE63, including microwave spectra and images from NoRH at 17 and 34 GHz, SSRT at 5.7 GHz, and TRACE in 1600 Å has led to the following results. A flare ribbon overlapped with the sunspot umbra, which is typical of large particle events. Atypical were: i) long duration of the flare of more than one hour; ii) moderate intensity of a microwave burst, about 104 sfu; iii) low peak frequency of the gyrosynchrotron spectrum, around 6 GHz; and its insensitivity to the flux increase by more than one order of magnitude. This was accompanied by a nearly constant ratio of the flux emitted by the volume in the high-frequency part of the spectrum to its elevated low-frequency part determined by the area of the source. With the self-similarity of the spectrum, a similarity was observed between the moving microwave sources and the brightest parts of the flare ribbons in 1600 Å. Comparison of the 17 GHz and 1600 Å images has confirmed that the microwave sources were associated with multiple flare loops, whose footpoints appeared in ultraviolet as intermittent bright kernels. To understand the properties of the event, we simulated its microwave emission using a system of several homogeneous gyrosynchrotron sources above the ribbons. The scatter between the spectra and sizes of the individual sources is determined by the inhomogeneity of the magnetic field within the ribbons. The microwave flux is mainly governed by the magnetic flux passing through the ribbons and the sources. An apparent simplicity of microwave structures is caused by a poorer spatial resolution and dynamic range of the microwave imaging. The results indicate that microwave manifestations of accelerated electrons correspond to the structures observed in thermal emissions, as well-known models predict.

Authors: V. Grechnev, A. Uralov, V. Kiselev, A. Kochanov
Projects: None

Publication Status: Accepted for publication in Solar Physics.
Last Modified: 2016-11-30 12:19
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The 26 December 2001 Solar Event Responsible for GLE63. I. Observations of a Major Long-Duration Flare with the Siberian Solar Radio Telescope  

Alexey Kochanov   Submitted: 2016-09-15 05:21

Ground Level Enhancements (GLEs) of cosmic-ray intensity occur, on average, once a year. Due to their rareness, studying the solar sources of GLEs is especially important to approach understanding their origin. The SOL2001-12-26 eruptive-flare event responsible for GLE63 seems to be challenging in some aspects. Deficient observations limited its understanding. Analysis of extra observations found for this event provided new results shading light on the flare. This article addresses the observations of this flare with the Siberian Solar Radio Telescope (SSRT). Taking advantage of its instrumental characteristics, we analyze the detailed SSRT observations of a major long-duration flare at 5.7 GHz without cleaning the images. The analysis confirms that the source of GLE63 was associated with an event in active region 9742 that comprised two flares. The first flare (04:30-05:03 UT) reached a GOES importance of about M1.6. Two microwave sources were observed, whose brightness temperatures at 5.7 GHz exceeded 10 MK. The main flare, up to the M7.1 importance, started at 05:04 UT, and occurred in strong magnetic fields. The observed microwave sources reached about 250 MK. They were not static. Having appeared on the weaker-field periphery of the active region, the microwave sources moved toward each other nearly along the magnetic neutral line, approaching a stronger-field core of the active region, and then moved away from the neutral line like expanding ribbons. These motions rule out an association of the non-thermal microwave sources with a single flaring loop.

Authors: V.V. Grechnev, A.A. Kochanov
Projects: None

Publication Status: Accepted for publication in Solar Physics (2016)
Last Modified: 2016-09-17 07:04
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Imaging of the solar atmosphere by the Siberian Solar Radio Telescope at 5.7 GHz with an enhanced dynamic range  

Alexey Kochanov   Submitted: 2013-10-16 23:14

The Siberian Solar Radio Telescope (SSRT) is a solar-dedicated directly-imaging interferometer observing the Sun at 5.7 GHz. The SSRT operates in the two-dimensional mode since 1996. The imaging principle of the SSRT restricts its opportunities in observations of very bright flare sources, while it is possible to use `dirty' images in studies of low-brightness features, which do not overlap with side lobes from bright sources. The interactive CLEAN technique routinely used for the SSRT data provides imaging of active regions but consumes much time and efforts and does not reveal low-brightness features below the CLEAN threshold. The newly developed technique combines the CLEAN routine with the directly-imaging capability of the SSRT and provides clean images with an enhanced dynamic range automatically. These elaborations considerably extend the range of tasks, which can be solved with the SSRT. We show some examples of the present opportunities of the SSRT and compare its data with the images produced by the Nobeyama Radioheliograph at 17 GHz as well as observations in different spectral ranges.

Authors: Alexey Kochanov, Sergey Anfinogentov, Dmitry Prosovetsky, George Rudenko, Victor Grechnev
Projects: None

Publication Status: PASJ (accepted)
Last Modified: 2013-10-17 14:37
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Abstracts by Author
The 26 December 2001 Solar Eruptive Event Responsible for GLE63. II. Multi-Loop Structure of Microwave Sources in a Major Long-Duration flare
The 26 December 2001 Solar Event Responsible for GLE63. I. Observations of a Major Long-Duration Flare with the Siberian Solar Radio Telescope
Imaging of the solar atmosphere by the Siberian Solar Radio Telescope at 5.7 GHz with an enhanced dynamic range

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MSU Solar Physics.
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