ar X iv : a st ro - p h / 06 02 23 1 v 1 1 0 Fe b 20 06 Flux upper limit of gamma - ray emission by GRB 050713 a from MAGIC Telescope observations

The long-duration GRB050713a was observed by the MAGIC Telescope, 40 seconds after the burst onset, and followed up for 37 minutes, until twilight. The observation, triggered by a SWIFT alert, covered energies above ≈ 175 GeV. Using standard MAGIC analysis, no evidence for a gamma signal was found. As the redshift of the GRB was not measured directly, the flux upper limit, estimated by MAGIC, is still compatible with the assumption of an unbroken power-law spectrum extending from a few hundred keV to our energy range. Subject headings: gamma rays: bursts — gamma rays: observations Universität Würzburg, Germany Institut de F́ısica d’Altes Energies, Barcelona, Spain Institute for Particle Physics, ETH Zurich, Switzerland Universidad Complutense, Madrid, Spain Universitat Autònoma de Barcelona, Spain Fachbereich Physik, Universität Dortmund, Germany Max-Planck-Institut für Physik, München, Germany Dipartimento di Fisica, Università di Padova, and INFN Padova, Italy Dipartimento di Fisica, Università di Udine, and INFN Trieste, Italy Division of Experimental Physics, University of Lódź, Poland Yerevan Physics Institute, Cosmic Ray Division, Yerevan, Armenia Tuorla Observatory, Piikkiö, Finland Institut für Physik, Humboldt-Universität zu Berlin, Germany University of California, Davis, USA Dipartimento di Fisica, Università di Siena, and INFN Pisa, Italy Dipartimento di Fisica, Università di Trieste, and INFN Trieste, Italy Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria Dipartimento di Fisica, Università di Pisa, and INFN Pisa, Italy Institut de Ciències de l’Espai, Barcelona, Spain deceased