Image credit: HAWCCheers of celebration erupted in March 2015 as the High-Altitude Water Cherenkov (HAWC) Gamma- Ray Observatory was formally inaugurated on the slopes of the Sierra Negra volcano in the State of Puebla, Mexico.  The inaugural ceremony marked the completion of HAWC, the latest tool for mapping the northern sky and studying the universe’s violent explosions of supernovae, which are neutron star collisions and active galactic nuclei that produce high-energy gamma rays and cosmic rays that travel large distances, making it possible to see objects and events far outside our galaxy.  

This extraordinary observatory uses a unique detection technique that differs from the classical astronomical design of mirrors, lenses, and antennae.  From its perch on top of the highest accessible peak in Mexico, HAWC observes TeV gamma rays and cosmic rays with an instantaneous aperture that covers more than 15% of the sky.  The detector is exposed to two-thirds of the sky during a 24-hour period.  The observatory's ability to operate continuously and its location at 14,000 feet above sea level allow HAWC to observe the highest energy gamma rays arriving anywhere within its field of view.

Brenda Dingus, the principal investigator of the U.S. Department of Energy (DOE) funding for HAWC and a research fellow at Los Alamos National Laboratory (LANL), says, “The HAWC Observatory will detect the highest energy photons ever observed.”  The discovery potential is enormous.  According to HAWC, one of the major strengths of an all-sky monitor is its ability to discover “new classes of objects unobserved at other wavelengths."  HAWC will investigate solar energetic particles, molecular clouds, and nearby galaxies, only a few of the topics which it intends to explore.

Describing HAWC’s detectors, LANL writes:  

Each of HAWC’s detectors is a huge tank containing 50,000 gallons of ultrapure water with four light sensors anchored to the floor.  When gamma rays or cosmic rays reach Earth’s atmosphere they set off a cascade of charged particles, and when these particles reach the water in HAWC’s detectors, they produce a cone-shaped flash of light known as Cherenkov radiation.

The light sensors record each flash of Cherenkov radiation inside the detector tanks.  By comparing nanosecond differences in arrival times at each light sensor, scientists can reconstruct the angle of travel for each particle cascade.  The intensity of the light indicates the primary particle’s energy, and the pattern of detector hits can distinguish between gamma rays and cosmic rays.  With 300 detectors spread over nearly three football fields, HAWC is able to ‘see’ these events in relatively high resolution.

The HAWC is the successor to the Milagro Gamma-Ray Observatory in New Mexico, which was also based around the principle of detecting gamma-rays indirectly using the water Cherenkov method.  LANL scientists indicate that the HAWC experiment is more than 10 times more sensitive than the Milagro experiment was, and it will detect many new astrophysical accelerators.  

The HAWC project is a unique collaboration of thirty academic institutions and one hundred scientists from the United States and Mexico.  The National Science Foundation, the DOE Office of Science, and Los Alamos National Laboratory provided funding for the United States’ participation in the HAWC project.  Mexico’s primary funder is The Consejo Nacional de Ciencia y Tecnologia.

Visit the DOE Science Showcase and In the OSTI Collections: Supernovae by Dr. William Watson to see how DOE high-energy astrophysics researchers and their collaborators are making major advances in observing and understanding stellar explosions of all types giving us insight into the origins of our universe.  OSTI provides free access to DOE research and development results from the myriad of DOE research endeavors through leading-edge products including SciTech Connect, DOE PAGES^Beta, DOE Data Explorer, DOepatents and ScienceCinema.