34th Solar Physics Division Meeting, June 2003
Session 15 Flares and Microflares I
Oral, Wednesday, June 18, 2003, 1:30-3:30pm, Auditorium

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[15.04] Study of Microflares at Hard X-ray and Microwave Wavelengths

J. Qiu, D. E. Gary, C. Liu, H. Wang (NJIT)

We present the preliminary results of studying microflares at hard X-ray and microwave wavelengths which are observed by Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Owens Valley Solar Array (OVSA). Among over 700 microflare bursts that are observed by RHESSI during the open-shutter mode from May to September in 2002, more than 200 fall into the OVSA observing time window. In this study, we analyze the first set of about 130 events jointly observed by the two instruments. These events are predominantly detected by RHESSI in the energy range below 15 keV. They are mostly accompanied by a minor increase in GOES flux below B5 level, but the time profiles at >10keV peak earlier than GOES flux by tens of seconds. By examining the lightcurves and dynamic spectra at hard X-ray and radio wavelengths, we find that more than 40% of the RHESSI bursts are unambiguously identified as microwave bursts, with the peak flux ranging from a few to several tens of solar flux units and the peak frequency at greater than 5 GHz. These results are indications of non-thermal features of the microflare events. We also discuss the distribution of microflares in quiet-Sun and active regions, the temporal and spatial relationship between microflares and major flares, and the spectral properties of microflares in comparison with major flares.

This work is supported by the NASA grant NAG5-10212.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.