TeV GAMMA-RAY SURVEY OF THE NORTHERN HEMISPHERE SKY USING THE MILAGRO OBSERVATORY

摘要

Milagro is a water Cerenkov extensive air shower array that continuously monitors the entire overhead sky in the TeV energy band. The results from an analysis of ～3 yr of data (2000 December-2003 November) are presented. The data have been searched for steady point sources of TeV gamma rays between declinations of 1.1° and 80°. Two sources are detected, the Crab Nebula and the active galaxy Mrk 421. For the remainder of the northern hemisphere, we set 95% confidence level (CL) upper limits between 275 and 600 mcrab (4.8 x 10~(-12) to 10.5 x 10~(-12) cm~(-2) s~(-1)) above 1 TeV for source declinations between 5° and 70°. Since the sensitivity of Milagro depends on the spectrum of the source at the top of the atmosphere, the dependence of the limits on the spectrum of a candidate source is presented. Because high-energy gamma rays from extragalactic sources are absorbed by interactions with the extragalactic background light, the dependence of the flux limits on the redshift of a candidate source are given. The upper limits presented here are over an order of magnitude more stringent than previously published limits from TeV gamma-ray all-sky surveys.