Hard X-ray radiation from solar flares in the second half of 2001: Preliminary results of the SPR-N experiment onboard the Coronas-F satellite

The first results of the experiment with the SPR-N hard X-ray (20-100 keV) polarimeter onboard the Coronas-F observatory (the experiment started on August 15, 2001) are presented. Hard X-ray radiation was detected from several solar flares. The spectral and temporal parameters were determined and the polarization was estimated. Comparison with the GOES observations of thermal X-ray radiation shows that hard X-ray bursts occur at the growth phase of the thermal radiation and that they are associated with the bremsstrahlung of energetic electrons precipitating into the solar atmosphere.