Time‐Resolved Spectroscopy of RHESSI GRBs

Time‐resolved spectroscopy may help to determine the still unknown emission mechanism which produces prompt gamma‐ray burst spectra. Prompt spectra evolve significantly over timescales much shorter than the total burst duration. It has been proposed that this evolution is due to the presence of thermal components which are masked in time‐integrated fits. We perform systematic spectral fitting of time‐resolved spectra for bright GRBs observed by RHESSI. We compare the effectiveness of phenomenological and quasi‐thermal models over RHESSI’s broad energy band (30 keV–17 MeV). The simplest quasi‐thermal model, a black body plus a power law, is disfavored relative to the Band function. Quasi‐thermal models with more realistic nonthermal components will be required to successfully reproduce the RHESSI data.