ARGO-YBJ constraints on very high energy emission from GRBs

The ARGO-YBJ experiment is designed for very high energy gamma-astronomy and cosmic ray researches. Due to the full coverage of a large area (5600 m^2) with resistive plate chambers at a very high altitude (4300 m a.s.l.), the ARGO-YBJ detector is used to search for transient phenomena, such as gamma-ray bursts (GRBs). Because the ARGO-YBJ detector has a large field of view ( about 2 sr) and is operated with a high duty cycle (>90%), it is one of the best ground-based GRB surveying apparatuses. Working at a relatively high energy threshold around a few hundreds of GeV, the ARGO-YBJ detector is operated in searches for high energy GRBs following alarms set by satellite-borne observations at lower energies. In this paper, the sensitivity of the ARGO-YBJ detector for GRB detection is estimated. Upper limits to fluence with 99% confidence level for 30 GRBs inside the field of view from June 2006 to January 2009 are set in the two energy ranges 10 GeV - 100 GeV and 10 GeV-1 TeV