This is a collaborative award to support the scientists who will work on the construction, commissioning and initial analysis of data from the High Altitude Water Cherenkov (HAWC) gamma-ray observatory being built at the Sierra Negra in Mexico. The HAWC collaboration consists of 14 US and 11 Mexican institutions. 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 a water Cherenkov air-shower detector consisting of 300 large water tanks. The tanks will be densely packed to cover an area of about 20,000 square meters. The goal is to begin taking data while the array is under construction and to have the full detector online within approximately three years.
Broader Impacts: HAWC is an all-sky instrument that will serve as a TeV "finder" telescope for Imaging Atmospheric Cherenkov Telescopes (IACTs) and IceCube and will have the sensitivity to extend the measurement of satellite-discovered sources to TeV. 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 project has developed an outreach video about HAWC and web materials about HAWC and Particle Astrophysics in both Spanish and English.
The High-Altitude Water Cherenkov (HAWC) TeV Gamma-Ray Observatory is currently under construction at a site about two hours' drive east of Puebla, Mexico on the Sierra Negra plateau (4100 m a.s.l.). HAWC is unique among TeV gamma-ray instruments in that it can observe large portions of the sky simultaneously, and covers half the sky every 24 hours. Therefore, the detector is particularly well-suited to measure extended and large-scale structures in the sky such as diffuse gamma-ray emission in our Galaxy and large- and small-scale anisotropies in the arrival directions of cosmic rays that continuously bombard Earth from Space. Discoveries of other extended unidentified objects at TeV energies, for example collocated with the famous "Fermi Bubbles," are also possible and may lead to new interpretations of these structures that probe the past activity of a supermassive black hole at the center of our Galaxy. The construction of HAWC is expected to be complete by Fall 2014. Data are already being collected during construction with an increasingly sensitive detector allowing for synchronous observations with instruments at other wavebands like the Fermi Space Telescope. The backbone of an experiment like the HAWC Observatory is its calibration system. Calibration is critical because it ensures for example that measurements of the instrument are accurate to better than 1 billionth of a seconds. Stable performance of the calibration system over time is crucial for a long term endeavor such as HAWC so that data from several years of operation can be compared. With the help of the NSF support for this project the HAWC calibration system was designed, tested at Michigan Tech, and installed at the high altitude site in Mexico. Since about a year it has been operated there remotely and in a stable mode. Analysis of the calibrated data set reveals significant anisotropies in the arrival directions of cosmic rays, both on small and large angular scales. The attached figure shows the very first publicly presented all-sky TeV gamma-ray map of the HAWC Observatory in celestial coordinates based on about three months of data taking. Red and yellow regions represent locations of enhanced gamma-ray emission and a concentration of these emission regions is visible along the Milky Way of our Galaxy. (The Milky Way region is indicated by the two dashed border lines, the location of the galactic center is marked by the black dot.). The gamma- and cosmic-ray data collected by the HAWC Observatory will be studied in more detail in the years to come.
