A solar burst submillimeter only spectral component during a GOES M class flare

CRISTIANI, G.D.; GIMÉNEZ DE CASTRO, C.G.; MANDRINI, C.H.; MACHADO, M.E.; DE BENEDETTO E SILVA, I.; KAUFMANN, P.; ROVIRA, M.G.

Montreal

Congreso; 37th COSPAR Scientific Assembly; 2008

COSPAR

Since the installation of submillimeter solar radio telescopes, a new spectral burst component was discovered at frequencies above 100 GHz, creating the THz bursts category. In all the reported cases, the events are of X class flares and the THz component was increasing. We report for the first time an M class flare which shows a submillimeter radio spectral component different from the microwaves classical burst one. In Active Region NOAA 10226 occurred two successive flares of 2 minute duration and delayed by 2 minutes, starting at around 13:15 UT and with an M 6.8 maximum intensity in Soft X-rays. Submillimeter flux density from the Solar Submillimeter Telescope (SST) are used in addition to microwave total Sun patrol telescope observations. Images with Halpha filters from the HASTA telescope and in the extreme UV from the EIT are used to characterize the flaring region. An extensive analysis of the magnetic topology evolution is derived from MDI magnetograms and used to constraint the solution space of the possible emission mechanisms. The submillimeter component is observed at 212 GHz only. We have upper limits for the emission at 89.4 and 405 GHz which are smaller than the observed flux density at 212 GHz. The analysis of the magnetic topology reveals a very compact and complex system of arches that reconnects at a low height, while from the Soft X-Ray observations we deduce that the flaring area is compact and dense (n ? 1012 cm-3 ). Accordingly we find that the microwave emission comes from mildly relativistic electrons spiraling down to a 200 G magnetic field footpoint. A very small portion of these electrons are mirrored and reach the other footpoint which has a stronger magnetic field (2000 G). In this process they emit the synchrotron observed at submillimeter frequencies. The finding of a submillimeter only burst component in a medium size flare indicates that the phenomenon is more universal than shown until now. The detailed analysis of this event reveals the high complexity of the flaring region.