Search for GeV GRBs with the INCA experiment

INCA is an air shower array located at Mount Chacaltaya in Bolivia, at 5200 m a.s.l., searching for Gamma Ray Bursts of energy E > 1 GeV. The results presented here concern a GRB search made in correlation with 70 events reco rded by BATSE since December 1996 to August 1998. For every burst, the INCA counting rate has been studied both during the BATSE detection time and in 2 hours around. No significant excess has been found in any of the trials. Assuming for the burst a power low energy spectrum extending up to 1 TeV w ith a slope alpha = -2 and a time duration of 10 s, the obtained 1 GeV divi ded by 1 TeV energy fluence upper limits range fi om 5.3 10(-5) erg cm(-2) to 2.9 10(-2) erg cm(-2) depending on the event zenith angle.