Multiple-loop structure of a solar flare from Microwave, EUV and X-ray Imaging Data

Abstract

We present the results of an analysis of a flare event of importance M2.8 that occurred at 00:56 UT 28 August 1999. The analysis is based upon observations made with the Nobeyama radioheliograph (NoRH) and polarimeters (NoRP), TRACE, SOHO/MDI, EIT, and Yohkoh/SXT. The images show a very complex flaring region. Pre-flare TRACE and EIT images at 00:24 UT show a small brightening in the region before the flare occurred. The active region in which the flare occurred had evolving magnetic fields, and new magnetic flux seems to have emerged. The X-ray and radio time profiles for this event show a double-peaked structure. The polarimeter data showed that the maximum radio emission (1200 s.f.u.) occurred at 9.4 GHz. At 17 GHz the NoRH images appear to show four different radio sources including the main spot and the main flare loop. Most of the microwave emission seems to originate from the main flare loop. Comparison of BATSE and microwave time profiles at 17 and 34 GHz from the main sunspot source shows that these profiles have similar structures and they coincide with the hard X-ray peaks. The maximum of the flare loop emission was delayed by 10 s relative to the second maximum of the sunspot associated flare emission. Analysis of SXT images during the post-flare phase shows a complex morphology – several intersecting loops and changes in the shape of the main flare loop.