This award will provide funds for the construction of the High Altitude Water Cherenkov (HAWC) gamma-ray observatory to be built at Sierra Negra in Mexico. The costs for hardware, engineering, and contract (nonscientist) labor to build HAWC are being provided here. The observations of HAWC will probe the most extreme environments in the Universe, providing a unique view of non-thermal processes in the Galaxy and beyond. The key science goals of HAWC are to: (a) Measure the spectrum of Galactic sources to the highest energies; (b) Map the Galactic diffuse gamma-ray emission from 1 TeV to 100 TeV measuring the cosmic-ray flux and spectrum across the Galaxy; (c) Study transient emission from active galactic nuclei (AGN); (d) Monitor the sky for 100 GeV emission from gamma-ray bursts; and (e) Search for new TeV physics with HAWC's unbiased sky survey. HAWC measurements have the potential to shed light on the fundamental symmetries of nature, including the search for Lorentz violation at extreme energies, the search for the dark matter in the universe, and the direct detection of massive relic particles.
HAWC is an array consisting of 250 large water tanks, each instrumented with three photomultiplier tubes (PMTs) mounted on the bottom of the tank. The tanks will cover an area of ~20,000 square meters. The expanded detection, increased altitude and optical isolation of the detector elements lead to a 15-fold increase in sensitivity relative to Milagro, which performed the deepest wide-field survey of the TeV sky to date. Refinement of the design and cost has been achieved through prototyping and deploying a test array at the HAWC site. The cost estimate and design sensitivity have stayed roughly constant through the development process. The goal is to begin taking data while the array is under construction and to be online within approximately three years. This will allow HAWC to run while the Fermi mission is ongoing.
Broader Impacts: HAWC is an all-sky instrument that will have the sensitivity to extend the measurement of satellite-discovered sources to TeV energies. HAWC will build on the strong outreach record of Milagro to bring this exciting field of research to students and the general public. Since HAWC is a joint US-Mexican project, this will be an excellent opportunity to attract talented Hispanic students to the field of Particle Astrophysics and to Physics in general. The group has developed an outreach video about HAWC and web materials about HAWC and Particle Astrophysics in both Spanish and English.
