Observation of TeV Gamma Rays from the Crab Nebula with Milagro Using a New Background Rejection Technique

The recent advances in TeV gamma-ray astronomy are largely the result of the ability to differentiate between extensive air showers generated by gamma rays and hadronic cosmic rays. Air Cerenkov telescopes have developed and perfected the ‘ ‘ imaging ’ ’ technique over the past several decades. However, until now no background rejection method has been successfully used in an air shower array to detect a source of TeV gamma rays. We report on a method to differentiate hadronic air showers from electromagnetic air showers in the Milagro gamma-ray observatory, based on the ability to detect the energetic particles in an extensive air shower. The technique is used to detect TeV emission from the Crab Nebula. The flux from the Crab Nebula is estimated to be 2:68ð0:42stat 1:4sysÞ 107ðE=1 TeVÞ2:59 m2 s1 TeV1, where the spectral index is assumed to be as given by the HEGRA collaboration. Subject headings: gamma rays: observations — instrumentation: detectors —