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R.S. Miller (Los Alamos National Laboratory), Milagro Collaboration
The Milagro Gamma-Ray Observatory is the first instrument capable of performing a sky survey at energies from ~500 GeV to >10 TeV - a relatively uncharted range of the electromagnetic spectrum. Located in northern New Mexico, Milagro will be capable of detecting steady, periodic, and transient sources from the Northern Hemisphere sky. With its large detector area (5000 m2), wide field-of-view (~1 sr), and high duty-cycle (~100%), Milagro is a unique application of water Cherenkov technology. This detection technique also allows the detetor to be operated in a ``scaler-mode'' which reduces the energy threshold to the GeV regime. The full-scale observatory is now in a continuous data taking mode.
A prototype of the Milagro detector was operational from February 1997 to April 1998. This prototype was the first air-shower array to detect a gamma-ray source, the active galaxy Markarian 501. Another highlight is the possible detection of solar energetic particles coincident with a Coronal Mass Ejection (CME) implying the presence of >10 GeV particles; this observation may place severe limits on the acceleration of high energy particles in the solar-terrestrial neighborhood. Previous air-shower arrays have also studied the cosmic ray shadow of the moon. At TeV energies the paths of cosmic rays are bent by the geo-magnetic fields leading to the displaced moon shadow clearly observed in the protoype array. A search for an anti-moon shadow is ongoing and will be used to set limits on the anti-matter content of the high energy cosmic ray flux.
Initial results and the status of the completed Milagro Observatory will also be discussed.
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