The gamma-ray sky as seen with HAWC

Abstract

Abstract. The High-Altitude Water Cherenkov (HAWC) TeV Gamma-Ray Observatory located at a site about two hours drive east of Puebla, Mexico on the Sierra Negra plateau (4100 m a.s.l.) was inaugurated in March 2015. The array of 300 water Cherenkov detectors can observe large portions of the sky simultaneously and, with an energy range of 100 GeV to 100 TeV, is currently one of the most sensitive instruments capable of probing particle acceleration near PeV energies. HAWC has already started science operation in the Summer of 2013 and preliminary sky maps have been produced from 260 days of data taken with a partial array. Multiple > 5 σ (pretrials) hotspots are visible along the galactic plane and some appear to coincide with known TeV sources from the H.E.S.S. catalog, SNRs and molecular cloud associations, and pulsars wind nebulae (PWNe). The sky maps based on partial HAWC array data are discussed as well as the scientific potential of the completed instrument especially in the context of multi-wavelengths studies. The HAWC TeV gamma-ray observatoryThe High-Altitude Water Cherenkov (HAWC) telescope is a continuously operating, wide field of view observatory sensitive to gamma rays and cosmic rays in the energy range of 50 GeV to 100 TeV. The telescope is capable of performing unbiased searches for transients to initiate multi-messenger observations. After five years of operation it will have accumulated an exposure of about 100 km 2 hr on more than half of the sky. As a wide-fieldof-view instrument the HAWC observatory is particularly well suited to measure large scale and extended structures such as the Fermi bubble structures or diffuse emission from the Galactic plane. HAWC combines the advantage of possessing the large duty cycle and field of view of space telescopes with the sensitivity to TeV energies. Thereby it provides a complementarity to imaging air Cherenkov telescope like VERITAS, MAGIC, and H.E.S.S., which are characterized by a smaller field of view but better angular resolution.Construction of the HAWC observatory began in 2012 and was completed in 2015. The observatory is located at 4100 m a.s.l. and 18• 59'41" N 97• 18'30.6" W at Sierra Negra near Pico de Orizaba in Mexico. It consists of 300 water Cherenkov detector (WCD) stations covering an area of 22,000 m 2 . Each WCD is 7.3 m wide and 4.5 m high and contains 200,000 L of purified water and four upward-facing photomultiplier tubes (PMT) attached to the bottom of each WCD: one high-quantum efficiency 10-inch Hamamatsu R7081-MOD PMT at the center and three 8-inch Hamamatsu R5912 PMTs at 1.8 m from the center [1]. Over one year of exposure, the completed HAWC array is expected to be sensitive to pure power law spectra at a level of 5 × 10 −13 cm −2 sec −1 (∼ 50 mCrab) a e-mail: petra@mtu.edu above 2 TeV over 5 sr (40%) of the sky [2]. Simulation studies predict an energy dependent angular resolution of between 0.1 • (at highest energies) and 0.8The reconstruction of the precise direction of a primary gamma ray relies on properly calibrated ...