WoP-MMA: Multi-TeV, Multi-Messenger, and Multi-Wavelength Particle Astrophysics with HAWC

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. This award supports scientists at Pennsylvania State University doing research with data collected with the HAWC observatory. The most significant result from the Penn State group is the identification of the highest-energy sources ever observed in our Galaxy. These objects can accelerate cosmic rays to energies about ten times higher than any particles produced using man-made particle colliders on Earth. The Penn State group is also actively engaged in education and outreach activities. As part of this program, an online data repository and display has been developed that makes the HAWC data accessible to the broad public.

Two very distinctive features of the HAWC Observatory are the continuous observations and the large field of view, which are vital to multi-messenger astrophysics of the northern sky. These make HAWC particularly important for the detection of very high energy gamma rays from extended regions and for the continuously survey of 2/3 of the sky. As an example of these capabilities, HAWC captured the first wide-angle view of very-high-energy light emanating from two rapidly spinning stars. The fresh perspective on these stellar neighbors casts serious doubt on one possible origin for a mysterious excess of particles near Earth whose origin has tantalized scientists in the last decade. These measurements demonstrate the capability of the HAWC observatory to detect such very extended objects. Relatively close galactic objects, like these two pulsars, appear so extended that one can only see them with an instrument with a wide field-of-view. Data from the HAWC observatory provides a unique and complementary view of these very extended sources that is not possible with the more pointed gamma-ray telescopes. Another important example of HAWC's capabilities in the awarded program is the continued search for the first galactic PeVatrons, a cosmic-ray accelerator capable of accelerating protons to PeV energies. Recent observations of the gamma-ray emission from the supernova remnant G106.3+2.7, Galactic microquasar SS 433 and HAWC discovered a gamma-ray source- HAWC J1825-134 – indicate spectra that continue well past 100 TeV. This implies production by relativistic protons with energies up to at least 800 TeV, or by relativistic electrons with energies up to at least 270 TeV. The data collected with the HAWC observatory bring us significantly closer to finding the first cosmic PeVatrons and understanding their nature. This project advances the goals of the NSF Windows on the Universe Big Idea.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.