Extragalactic Astrophysics and Cosmic-Ray Physics with HAWC

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Gamma-rays are the highest energy form of electromagnetic radiation. Observations of astrophysical gamma-rays serve as probes of physical conditions and processes in the most extreme environments throughout the Universe, and can be used to test fundamental physics. The High Altitude Water Cherenkov (HAWC) observatory, located on the slopes of the Sierra Negra in Mexico, is a ground-based facility designed with unique capabilities to observe very high energy gamma-rays. HAWC is also capable of observing cosmic-rays, which are highly energetic sub-atomic particles that travel near the speed of light. The origin and acceleration mechanisms of cosmic rays are unknown. The highest energy cosmic rays likely originate in extreme astrophysical phenomena outside our galaxy. This award supports scientists at the University of Wisconsin in the analysis of gamma-ray and cosmic-ray data collected with HAWC. They will study flares from extragalactic gamma-ray sources and measure the anisotropy in the arrival directions of cosmic rays. The group will partner with the "El Universo es Tuyo" program in outreach and education programs for local Spanish-speaking students. With its large instantaneous field of view and continuous operations HAWC surveys two-thirds of the sky every day. The University of Wisconsin group will study flaring activity in extragalactic gamma-ray sources and measure the cosmic-ray anisotropy in the TeV to PeV energy range. The group has developed and implemented a flare monitor program that analyzes HAWC data in real-time to search for flaring activity. Rapid alerts are sent out to trigger searches by other telescopes at other wavelengths or facilities that observe cosmic rays or neutrinos. The group will continue to operate and further develop the flare monitor, and they will analyze the data taken during flaring events. Using new methods and combining HAWC skymaps with maps from the IceCube neutrino observatory at the South Pole, the group will study cosmic-ray anisotropy across the northern and southern hemispheres to address the long-standing discrepancy in the observed and expected dipole strength.