Milagro Search for Very High Energy Emission from Gamma‐Ray Bursts in the Swift Era

The recently launched Swift satellite is providing an unprecedented number of rapid and accurate Gamma‐Ray Burst (GRB) localizations, facilitating a flurry of follow‐up observations by a large number of telescopes at many different wavelengths. The Very High Energy (VHE, >100 GeV) regime has so far been relatively unexplored. Milagro is a wide field of view (2 sr) and high duty cycle (> 90%) ground‐based gamma‐ray telescope which employs a water Cherenkov detector to monitor the northern sky almost continuously in the 100 GeV to 100 TeV energy range. We have searched the Milagro data for emission from the most recent GRBs identified within our field of view. These include three Swift bursts which also display late‐time X‐ray flares. We have searched for emission coincident with these flares. No significant detection was made. A 99% confidence upper limit is provided for each of the GRBs, as well as the flares.