The 26 December 2001 Solar Event Responsible for GLE63. I. Observations of a Major Long-Duration Flare with the Siberian Solar Radio Telescope

TL;DR

This study analyzes a major long-duration solar flare associated with GLE63 using Siberian Solar Radio Telescope observations, revealing dynamic microwave source motions and their relation to active region magnetic fields.

Contribution

It provides detailed SSRT observations of the flare, showing microwave source movements and their implications for understanding GLE origins, which were limited in previous studies.

Findings

Microwave sources exceeded 10 MK brightness temperature.

Sources moved along the magnetic neutral line, indicating complex flare dynamics.

The flare involved two separate events in active region 9742.

Abstract

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.