The High-Altitude Water Cherenkov (HAWC) observatory in México: The primary detector

The High-Altitude Water Cherenkov (HAWC) observatory is a second-generation continuously operated, wide field-of-view, TeV gamma-ray observatory. HAWC and its analysis techniques build on experience of the Milagro experiment in using ground-based water detectors for astronomy. located Sierra Negra volcano M\'exico at an elevation 4100 meters above sea level. completed principal detector consists 300 closely spaced detectors, each equipped with four photomultiplier tubes to provide timing charge information reconstruct extensive air shower energy arrival direction. has been optimized observe transient steady emission from sources gamma rays within range several hundred GeV TeV. However, most showers detected are initiated by cosmic rays, allowing studies also be performed. This paper describes characteristics main array hardware.