RHESSI Microflares Statistics

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) provides unique sensitivity in the 3-15 keV energy range with an effective area ∼100 times larger then similar past instruments. Microflares have been observed with little emission above 15 keV due to extremely steep spectra (spectral index of ~8 with a low energy cutoff near 8 keV). Since the energy in non-thermal electrons is very sensitive to the value of the power law and the low energy cutoff, observations by RHESSI will give a better estimate of the total energy input into the corona. We present the first statistical analysis of RHESSI microflares during times with activity below GOES C Class and without solar type III radio storms. Currently, we have analyzed June 2002 and May 2003. Microflares are found through searching for peaks 3σ above background in the 6-12 keV data range. The fluxes in the 3-6 keV 12-25 keV, and 50-100 keV bands are also recorded. Statistics on the following flare characteristics are presented; max counts, total counts, duration, GOES level. We have also analyzed the equivalent WIND data set in search of correlated solar type III radio bursts. Initial results show that only a small number of RHESSI microflares are associated with interstellar type III radio bursts. This work was supported by NASA contract NAS5-98033.