Observing Gamma Ray Bursts with the RHESSI satellite

Abstract The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) was launched successfully on the 5th of February 2002 into a low Earth orbit. It is a NASA Small Explorer satellite designed to study hard X-rays and gamma-rays from solar flares. In addition, its lightly shielded array of 9 germanium detectors can see photons from high-energy sources throughout the Universe, in particular also from Gamma Ray Bursts (GRBs). With its wide field of view, RHESSI observes about one GRB per week, the sensitive energy band ranging from about 30 keV to 15 MeV. By presenting preliminary lightcurves and raw spectra from three very strong GRBs observed with RHESSI we demonstrate its high time and energy resolution. Since the arrival time and energy of each photon is recorded, combined time/energy studies, e.g. time dependent hardness ratios, can be studied.