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1. High-Energy Astrophysics with the HAWC Observatory Thomas Weisgarber for the HAWC Collaboration 14th High Energy Astrophysics Division Meeting Chicago, 17-21 August 2014 HAWC Extragalactic Gamma-Ray Science HAWC Galactic Gamma-Ray Science Extragalactic gamma rays at the TeV scale are predominantly produced by blazars, active galaxies with a jet aligned along the line of sight to Earth. Blazars are highly variable objects that often flare to many times their The Galactic plane is already evident in preliminary HAWC data, as shown in the all-sky map at the right. In this preliminary map, the Crab nebula, shown below left, has been detected at a significance of more than 10 sigma. quiescent emission [2]. HAWC has already detected the two nearest blazars, Markarian 421 and Markarian 501 (shown at right), and expects to detect many more. Science goals from the study of blazars include: • determination of the high-energy cutoff • measurement of the extragalactic background light • detection of extreme flares • joint observations with other TeV instruments to understand dynamics of the central engine • searching for the fingerprint of the intergalactic magnetic field Left: Spectra (top) and Fermi counts map overlaid with Milagro contours for the Fermi cocoon, a region of newly accelerated cosmic rays. The Fermi and Milagro spectra appear to be consistent. Right: Milagro, VERITAS, and ARGO-YBJ spectra of MGRO J2019+37. Skymap from [1]. HAWC will likely discover many new sources lying just below Milagro’s detection threshold. Gamma-Ray Bursts Gamma-ray bursts (GRBs) are extremely violent cosmic events known to produce gamma rays up to 100 GeV energies. Two independent systems enable HAWC to detect GRBs, the main data stream and a scaler system that monitors the total rate. Limits from HAWC on the recent GRB Real-Time Flare Monitor Since HAWC continuously monitors the entire overhead sky, it is capable of detecting flares as soon as they occur. An online flare-monitor system will be operational by the beginning of full-scale HAWC observations. Via this system, HAWC will issue alerts to the TeV and general astroparticle physics communities when significant flaring activity is detected in the TeV band. Both known and potential sources will be monitored. In addition to the above specific sources, HAWC will also study known TeV sources and search for new Galactic TeV sources, including: • supernova remnants • Galactic diffuse emission at TeV energy • known TeV binaries with uncertain duty cycles • pulsar wind nebulae • large, extended sources (challenging for pointed instruments) • and more! 130427A are shown at right for the partial detector. With the full array, the HAWC scaler system would permit a measurement of the expected spectrum. • See C. M. Hui’s presentation in Section 301.03 for further details on Galactic TeV science with HAWC The HAWC Observatory Fundamental Physics with HAWC Cosmic Rays with HAWC HAWC pursues a broad range of fundamental physics topics related to gamma-ray astrophysics. Included among these are: The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, pictured below, detects astrophysical gamma rays and cosmic rays in the energy range from 100 GeV to 100 TeV. Located at an elevation of 4,100 meters on the slopes of Sierra Negra in the Mexican state of Puebla, HAWC comprises an array of 300 water Cherenkov detectors (WCDs) covering an area of 22,000 square meters. Already in operation as a partial array for more than a year, HAWC is nearing completion and will soon enter full-scale operations. HAWC detects cosmic rays as well as gamma rays. As shown at right, cosmic rays absorbed by the moon create the most significant feature in the HAWC data, a deficit of events near the disc of the moon. Milagro, the predecessor to HAWC, discovered a small-scale anisotropy in the distribution of cosmic rays on the sky. With nearly 50 billion events collected, HAWC observes the regions A and B (indicated below) detected by Milagro, as well as a new Region C recently detected by ARGO-YBJ. • self-annihilating dark matter • decay of primordial black holes • tests of Lorentz invariance violation with variable high-energy sources • Q-balls Dark Matter Dark matter is of particular interest to HAWC, as certain objects such as galaxy clusters may produce a gamma-ray signal due to dark matter annihilation. The plot at the right depicts the sensitivity of HAWC to the Virgo cluster, showing that HAWC can produce competitive dark matter limits for high mass dark matter particles. HAWC Sensitivity HAWC has amassed enough events to generate a power spectrum of TeV cosmic rays (left). This power spectrum is in qualitative agreement with predictions that the small-scale anisotropy arises from turbulence in the particular realization of the Galactic magnetic field close to the solar system [3,4]. HAWC reconstructs the direction and energy of primary gamma rays and cosmic rays that initiate extensive air showers. Each WCD is instrumented with 4 photomultiplier tubes that measure the intensity and arrival time of Cherenkov light emitted by charged particles in the air shower as they pass through the detector (below left). With a duty cycle greater than 90% and an instantaneous field of view of 2 sr, HAWC conducts daily unbiased observations of the entire sky between -26° and 64° in declination. The sensitivity of HAWC along with many known TeV gamma-ray sources [5] appears below at the right. shower particles Effective area [m2] References Cherenkov photons HAWC improves over its predecessor, Milagro, in angular and energy resolution, as well as in gamma-hadron separation (left). As shown above, above 4 TeV, its one-year sensitivity to every source becomes equivalent to a 50-hour observation on a single source by Cherenkov telescopes such as VERITAS, HESS, and MAGIC. [1] Aliu, E. et al, ApJ 788, 78A (2014). [2] Tluczykont, M. et al, A&A 542A, 48T (2010). [3] Giacinti, G. & Sigl, G., Phys. Rev. Lett. 109, 071101 (2012). [4] Ahlers, M., Phys. Rev. Lett. 112, 021101 (2014). [5] http://tevcat.uchicago.edu Web: http://www.hawc-observatory.org Contact: weisgarber@physics.wisc.edu HAWC is a collaborative effort between institutions in the United States of America and Mexico.