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Milagro is a water-Cherenkov detector that observes the extended air showersproduced by cosmic gamma rays of energies E>100GeV. The effective area ofMilagro peaks at energies E~10TeV, however it is still large even down to a fewhundred GeV (~10m^2 at 100GeV). The wide field of view (~2sr) and high dutycycle (>90%) of Milagro make it ideal for continuously monitoring the overheadsky for transient Very High Energy (VHE) emissions. This study searched theMilagro data for such emissions. Even though the search was optimized primarilyfor detecting the emission from Gamma-Ray Bursts (GRBs), it was still sensitiveto the emission from the last stages of the evaporation of Primordial BlackHoles or to any other kind of phenomena that produce bursts of VHE gamma rays.Measurements of the GRB spectra by satellites up to few tens of GeV showed nosigns of a cutoff. Even though multiple instruments sensitive to $GeV/TeV$gamma rays have performed observations of GRBs, there has not yet been adefinitive detection of such an emission yet. One of the reasons for that isthat gamma rays with energies E>~100GeV are attenuated by interactions with theextragalactic background light or are absorbed internally at the site of theburst. There are many models that predict VHE gamma-ray emission from GRBs. Adetection or a constraint of such an emission can provide useful information onthe mechanism and environment of GRBs. This study performed a blind search ofthe Milagro data of the last five years for bursts of VHE gamma rays withdurations ranging from 100musec to 316sec. No GRB localization was provided byan external instrument. Instead, the whole dataset was thoroughly searched intime, space, and duration. No significant events were detected. Upper limitswere placed on the VHE emission from GRBs.

A Blind Search for Bursts of Very High Enery Gamma Rays with Milagro