Very high energy follow-up observations of GRBs detected by Fermi and Swift

In many theoretical models of gamma-ray bursts (GRBs) and their afterglows, the emission of photons above 100 GeV is predicted. The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope has detected delayed, high-energy emission (up to 90 GeV in the burst rest-frame) from several GRBs and no evidence of a high-energy spectral cutoff during the early afterglow phase of the burst has been found. Presented here are the results of follow-up observations with VERITAS, a ground-based telescope array sensitive to gamma-rays above 100 GeV, of GRBs detected by the Fermi and Swift satellites. These observations have not yielded a conclusive detection and the upper limits on very high energy (VHE, E>100 GeV) gamma-ray flux obtained from these observations are among the most constraining to date.