With its 300th detector tank in place, the High Altitute Water Cherenkov Observatory (HAWC) marked its completion on 20 Marth. Located at an altitude of 4100 m on the flank of the Sierra Negra, an extinct volcano east of Mexico City, the observatory keeps a constant lookout for high-energy gamma rays; data taking began in August 2013 with a partial array (see Physics Today, October 2013, page 22.
HAWC detects Cherenkov radiation from charged particles speeding through its 190 000-liter tanks of water. The particles originate from high-energy (100-GeV to 100-TeV) gamma rays colliding with the atmosphere.
Among the HAWC goals are to map TeV sources in the Milky Way and detect transient emissions from active galaxies and other sources. Unlike most Cherenkov telescopes, which are more sensitive but can only observe small patches of the sky, “we look at the entire overhead sky, so we have a...
