Search for ultrahigh-energy cosmic gamma-ray bursts on the Baksan underground scintillation telescope

Based on data from the Baksan underground scintillation telescope ( BUST) for the period 2001-2004, we searched for cosmic gamma-ray bursts (GRBs) at primary photon energies of 0.5 TeV or higher. We obtained constraints on the rate of bursts with durations of 1-10 s for fluences within the range 4.6 x 10(-3)-1.8 x 10(-2) erg cm(-2) in the declination band 30 degrees <= delta <= 80 degrees. We searched for ultrahigh-energy gamma rays from GRBs detected on spacecraft during and within +/- 2 h of the burst. No statistically significant excesses above the background of random coincidences were found. The derived constraints on the ultrahigh-energy gamma-ray fluence during GRBs lie within the range 4.6 x 10(-3)-3.7 x 10(-2) erg cm(-2).