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 range1-100 GeV in coincidence with the prompt emission detected bysatellites using the Astrophysical Radiation with Ground-basedObservatory at YangBaJing (ARGO-YBJ) air shower detector. Thanks to itsmountain location (Yangbajing, Tibet, People's Republic of China, 4300m above sea level), active surface (similar to 6700 m(2) of ResistivePlate Chambers), and large field of view (similar to 2 sr, limited onlyby the atmospheric absorption), the ARGO-YBJ air shower detector isparticularly suitable for the detection of unpredictable and shortduration events such as GRBs. The search is carried out using the"single particle technique," i.e., counting all the particles hittingthe detector without measurement of the energy and arrival direction ofthe primary gamma rays. Between 2004 December 17 and 2009 April 7, 81GRBs detected by satellites occurred within the field of view ofARGO-YBJ (zenith angle theta <= 45 degrees). It was possible to examine62 of these for > 1 GeV counterpart in the ARGO-YBJ data finding nostatistically significant emission. With a lack of detected spectra inthis energy range fluence upper limits are profitable, especially whenthe redshift is known and the correction for the extragalacticabsorption can be considered. The obtained fluence upper limits reachvalues as low as 10(-5) erg cm(-2) in the 1-100 GeV energy region.Besides this individual search for a higher energy counterpart, astatistical study of the stack of all the GRBs both in time and inphase was made, looking for a common feature in the GRB high-energyemission. No significant signal has been detected.