A solar burst with a spectral component observed only above 100~GHz during an M class flare

GERMÁN CRISTIANI; CARLOS GUILLERMO GIMÉNEZ DE CASTRO; CRISTINA HEMILSE MANDRINI; MARCOS EMILIO MACHADO; IGOR DE BENEDETTO E SILVA; PIERRE KAUFMANN; MARTA GRACIELA ROVIRA

Ciudad de San Juan

Congreso; 51va Reunión Anual de la Asociación Argentina de Astronomía; 2008

Asociación Argentina de Astronomía

We study the M6.8 class flare on 20 December, 2002, which shows a submillimeter radio spectral component different from the microwave classical burst. Two successive bursts occurred in active region (AR) 10226 around 13:15 UT. Sub-mm and microwave flux density data in addition to Halpha, UV, and soft X-ray observations are used to characterize the flaring region. The sub-mm component is only observed at 212 GHz. An extensive analysis of the magnetic field evolution is derived from full-disk magnetograms. The magnetic topology reveals a very compact and complex system of arches anchored in regions with magnetic field intensity differing by an order of magnitude that reconnects at low heights. Thus, we conclude that the microwave emission comes from mildly relativistic electrons spiraling down along the reconnected loops. A very small portion of the accelerated electrons can reach the footpoint with the stronger magnetic field (2000 G) and produce synchrotron emission, which is observed at sub-mm frequencies.