Abstract:
Without prior signal, an enormous amount of energy is released for seconds in Gamma-ray bursts (GRBs). The emitting regions can produce Very-High-Energy (VHE) gamma-ray photons of energy ~1011 eV during and after the burst. These VHE gamma-rays may be attenuated in the source or by the extragalactic background light (EBL). After a brief review on the current status of VHE observations of GRBs, the ground-based H.E.S.S. array of four imaging atmospheric Cherenkov telescopes (IACT), sensitive to VHE gamma-rays, is introduced. H.E.S.S. observations of 34 GRBs were carried out during 2003-2008. No evidence of VHE gamma-rays was found. Flux upper limits derived for GRB 030329 and GRB 060505 are compared and are found consistent with the synchrotron self-Compton flux calculated in the context of relativistic blast-wave model. The case of GRB 060602B where strictly simultaneous observations with H.E.S.S. throughout the GRB duration is highlighted. Some future prospects of VHE gamma-ray observations of GRBs are discussed.
Coffee and tea will be served 20 minutes prior to the seminar.