The detection of the Vbry High Energy (VHE) emission from Gamma Ray Bursts(GRBs) is desired,as it willprovide an unprecedented opportunity to enlighten the nature of the central engine and the interaction between the relativisticflow and the environment of the burst progenitor．Thanks to its large reflector size,high quantum efficiency photomultipliersand sophisticated trigger logic,the MAGIC telescope is currently the most sensitive detector at energies around 100 GeV．Inaddition,thanks to its fast repositioning time,MAGIC iS able to start the GRB follow-up observation,triggered by an alertfrom the GRB Coordinates Network(GCN),on average within 45 s after the burst onset To．In the past years of operationseveral simultaneous GRB observations of the prompt and early afterglow emission phase with satellite experiments wereperformed by MAGIC．However,until now without successful detection of VHEγ-rays above threshold energies>80 GeV．The computed upper limits are compatible with a power law extrapolation,where intrinsic fluxes are evaluated by taking intoaccount the attenuation due to the scattering in the metagalactic radiation field．
MAGIC LACT Cherenkov gamma-ray GRB
Markus Garczarczyk L.Angelo Antonelli Antonio La Barbera Denis Bastieri Stefano Convino Nicola Galante Markus Gaug Francesco Longo Valeria Scapin
Institut de Fisica dAltes Energies,Edifici Cn.UAB,08193 Bellaterra (Barcelona),Spain INAF Rome,Viale del Parco Mellini 84,00136 Rome,ItdIy INAF Palermo,Via Ugo La Matfa 153,90146 Palermo,Italy Universita degli Studi di Padova,via Marzolo 8,35131 Padova,Italy INAF Rome,viale del Parco Mellini 84,00136 Rome,Italy Max-Planck-lnstitut fur Physik,Fohringer Ring 6,80805 Munchen,Germany Instituto de Astrofisica de Canarias,via Lactea s/n,38205La Laguna,Tenerife,Spain INFN Trieste,via F.Valerio 2,I-34127 Trieste,Italy Universita degli Studi di Udine,via delle Scienze 208,I-33100 Udine,Italy