Observation of gamma ray bursts at very high energies with the MAGIC telescope

The detection of the Very High Energy (VHE) emission from Gamma Ray Bursts (GRBs) is desired, as it will provide an unprecedented opportunity to enlighten the nature of the central engine and the interaction between the relativistic flow and the environment of the burst progenitor. Thanks to its large reflector size, high quantum efficiency photomultipliers and sophisticated trigger logic, the MAGIC telescope is currently the most sensitive detector at energies around 100 GeV. In addition, thanks to its fast repositioning time, MAGIC is able to start the GRB follow-up observation, triggered by an alert from the GRB Coordinates Network (GCN), on average within 45s after the burst onset T0. In the past years of operation several simultaneous GRB observations of the prompt and early afterglow emission phase with satellite experiments were performed by MAGIC. However, until now without successful detection of VHE g-rays above threshold energies > 80 GeV. The computed upper limits are compatible with a power law extrapolation, where intrinsic fluxes are evaluated by taking into account the attenuation due to the scattering in the metagalactic radiation field.