SEARCH FOR GAMMA RAY BURSTS WITH THE ARGO-YBJ DETECTOR IN SCALER MODE

Abstract

We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100\nGeV in coincidence with the prompt emission detected by satellites using the\nAstrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ)\nair shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R.\nChina, 4300 m a.s.l.), active surface (about 6700 m**2 of Resistive Plate\nChambers), and large field of view (about 2 sr, limited only by the atmospheric\nabsorption), the ARGO-YBJ air shower detector is particularly suitable for the\ndetection of unpredictable and short duration events such as GRBs. The search\nis carried out using the "single particle technique", i.e. counting all the\nparticles hitting the detector without measurement of the energy and arrival\ndirection of the primary gamma rays.\n Between 2004 December 17 and 2009 April 7, 81 GRBs detected by satellites\noccurred within the field of view of ARGO-YBJ (zenith angle < 45 deg). It was\npossible to examine 62 of these for >1 GeV counterpart in the ARGO-YBJ data\nfinding no statistically significant emission. With a lack of detected spectra\nin this energy range fluence upper limits are profitable, especially when the\nredshift is known and the correction for the extragalactic absorption can be\nconsidered. The obtained fluence upper limits reach values as low as 10**{-5}\nerg cm**{-2} in the 1-100 GeV energy region.\n Besides this individual search for a higher energy counterpart, a statistical\nstudy of the stack of all the GRBs both in time and in phase was made, looking\nfor a common feature in the GRB high energy emission. No significant signal has\nbeen detected.\n