THE MILAGRO GAMMA-RAY OBSERVATORY

MILAGRO will be the first water-Cherenkov detector specifically built to study extensive air showers. It is being built in an existing man-m ade pond 60 m times 80 m by 8 m, located in the Jemez mountains near L os Alamos, NM. Unlike conventional air shower detectors, which sample less than 1% of the particles which reach detector level, MILAGRO will be totally sensitive to electrons, photons, hadrons, and muons hittin g the detector. The threshold of the MILAGRO detector is comparable to atmospheric Cherenkov detectors, however it has several advantages ov er these optical detectors. MILAGRO is operational 24 hours a day in a ll weather conditions and it has an open aperture which allows it to v iew the entire northern sky every day. These capabilities allow for a systematic all-sky survey to be done for the first time at these energ ies. MILAGRO will search for point sources of VHE gamma radiation, bot h steady and episodic. MILAGRO will measure the Crab spectrum with hig h significance and possibly locate a cut off in the spectrum. In addit ion, it will detect and measure the spectra from AGN's such as MRK 421 . MILAGRO will be the first VHE detector capable of recording Gamma Ra y Bursts at energies above 250 GeV. The physics merits of this detecto r together with its design and current status are discussed.