HR: 16:30h
AN: SH24A-03    [Abstracts]
TI: Nonthermal X-ray Microflares
AU: * Christe, S
EM: schriste@ssl.berkeley.edu
AF: Physics Department, University of California at Berkeley, Berkeley, CA 94720-7300 United States
AU: Rauscher, E
AF: Physics Department, University of California at Berkeley, Berkeley, CA 94720-7300 United States
AU: Krucker, S
AF: Space Sciences Lab, University of California at Berkeley, Berkeley, CA 94720-7450 United States
AU: Lin, R P
AF: Physics Department, University of California at Berkeley, Berkeley, CA 94720-7300 United States
AU: Lin, R P
AF: Space Sciences Lab, University of California at Berkeley, Berkeley, CA 94720-7450 United States
AB: The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) provides unique sensitivity in the 3-15 keV energy range, with an effective area $\sim$100 times larger than similar past instruments. Along with its high spectral resolution (1 keV) RHESSI is uniquely suited to study small events. Microflares have been observed by Benz & Grigis (2002) and Krucker et al. (2002) to have anomalously steep spectra ( spectral index between -5 and -8) extending down to $\sim$ 7 keV. Thermal emission is found to dominate below $\sim$ 7 keV. In many other respects, microflares show properties similar to larger flares. We present single event studies of different types of x-ray microflares. RHESSI observations during quiet times (04-May 10-14; GOES level low B class) reveal a set 5 microflares (>=A Class). These microflares show power law spectra (spectral index of $\sim$4-8) with little or no thermal emission in the 3-$\sim$7 keV energy range above the nonthermal part of the spectrum. Other microflares in the same GOES class range, however, have been found which show extremely hard spectra with emission up to 50 keV (power law index $\sim$2). At lower energies, emission is dominated by a hot thermal component (20 MK). This work was supported by NASA contract NAS5-98033.
UR: http://sprg.ssl.berkeley.edu/~schriste/welcome.php
DE: 7509 Corona
DE: 7514 Energetic particles (2114)
DE: 7519 Flares
DE: 7537 Solar and stellar variability
DE: 7554 X rays, gamma rays, and neutrinos
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting