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Premier New Gamma Ray Observatory Begins Operation

August 21, 2013

Lee Tune 301-405-4679

COLLEGE PARK, Md. – A joint U.S. and Mexican gamma ray observatory being built on the flanks of the Sierra Negra volcano in the Mexican State of Puebla has begun official operations. Led on the U.S. side by the University of Maryland, the observatory is only about one-third complete, but already it is the largest of its type in the world.

Deployment of tanks and counting house trailers on the HAWC platform as seen from the slope of the volcano Sierra Negra (April 2013). The volcano Pico de Orizaba is visible in the background. Gamma rays are the most energetic form of light (electro-magnetic radiation) and are produced by the most violent events and hottest regions of the universe: supernova star explosions, active galactic nuclei caused by super massive black holes and gamma ray bursts. Gamma rays also are thought to be correlated with the acceleration sites of charged cosmic rays, whose origins have been a mystery for nearly 100 years.

The HAWC (High-Altitude Water Cherenkov Observatory) facility is designed to observe the highest energy (TeV) gamma rays and cosmic rays with an instantaneous aperture that covers more than 15 percent of the sky. With this large field of view, the detector will be exposed to half of the sky during a 24-hour period.

"HAWC will be the world's premier wide-field TeV gamma ray observatory with between 10 and 15 times the sensitivity of previous generation wide-field gamma ray detectors such as Milagro," says UMD professor of physics Jordan Goodman, who is the Principal Investigator for the National Science Foundation HAWC construction grant that is funded through UMD and covers about half of the approximately $14 million cost of the construction. 

UMD physicist Andrew Smith is the HAWC project manager. UMD scientists Brian Baughman, Jim Braun and Josh Wood also are involved in the construction of HAWC and together with Goodman and Smith will help lead in the analysis of data from the observatory.

Detecting Gamma Rays
The HAWC observatory currently has some 111 detectors and will have a total of 300 when it is completed in 2014.When high-energy gamma rays enter the atmosphere they collide with and split air molecules into more particles and gamma rays. These in turn interact with more particles, losing energy, but creating new particles and gamma rays each time. This chain reaction results in a cascade, or shower, of particles and radiation that multiplies and expands outward all the way to the ground, where it reaches the HAWC's water Cherenkov detectors. The HAWC observatory currently has some 111 detectors and will have a total of 300 when it is completed in 2014.

When the gamma ray-caused cosmic cascade goes through the water-filled Cherenkov detectors, the cascade particles, traveling faster than the light inside the water, create an effect similar to a supersonic airplane producing a shock wave (the so-called sonic "boom"). But in this case, the particles produce a visible light trail instead of sound waves. These flashes are measured by light detectors located at the bottom of each Cherenkov detector. By computationally reconstructing the combined signals from all the detectors, it is possible for scientists to determine the energy, direction, time of arrival and the nature of the responsible gamma ray.

The new HAWC observatory is supported by numerous U.S. and Mexican institutions, including the National Science Foundation, the Los Alamos National Laboratory, the Department of National Energy, the University of Maryland, Consejo Nacional de Ciencia y Tecnología, the Universidad Nacional Autónoma de México, the Instituto Nacional de Astrofísica and the Óptica y Electrónica.