15 research outputs found
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Search for gamma-rays from the unusually bright GRB 130427a with the hawc gamma-ray observatory
The first limits on the prompt emission from the long gamma-ray burst (GRB) 130427A in the >100 GeV energy band are reported. GRB 130427A was the most powerful burst ever detected with a redshift z ≲ 0.5 and featured the longest lasting emission above 100 MeV. The energy spectrum extends at least up to 95 GeV, clearly in the range observable by the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, a new extensive air shower detector currently under construction in central Mexico. The burst occurred under unfavorable observation conditions, low in the sky and when HAWC was running 10% of the final detector. Based on the observed light curve at MeV-GeV energies, eight different time periods have been searched for prompt and delayed emission from this GRB. In all cases, no statistically significant excess of counts has been found and upper limits have been placed. It is shown that a similar GRB close to zenith would be easily detected by the full HAWC detector, which will be completed soon. The detection rate of the full HAWC detector may be as high as one to two GRBs per year. A detection could provide important information regarding the high energy processes at work and the observation of a possible cut-off beyond the Fermi Large Area Telescope energy range could be the signature of gamma-ray absorption, either in the GRB or along the line of sight due to the extragalactic background light
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Observation of small-scale anisotropy in the arrival direction distribution of TeV cosmic rays with HAWC
The High-Altitude Water Cherenkov (HAWC) Observatory is sensitive to gamma rays and charged cosmic rays at TeV energies. The detector is still under construction, but data acquisition with the partially deployed detector started in 2013. An analysis of the cosmic-ray arrival direction distribution based on 4.9 × 1010 events recorded between 2013 June and 2014 February shows anisotropy at the 10-4 level on angular scales of about 10°. The HAWC cosmic-ray sky map exhibits three regions of significantly enhanced cosmic-ray flux; two of these regions were first reported by the Milagro experiment. A third region coincides with an excess recently reported by the ARGO-YBJ experiment. An angular power spectrum analysis of the sky shows that all terms up to l = 15 contribute significantly to the excesses
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The HAWC Gamma-Ray Observatory: Sensitivity to Steady and Transient Sources of Gamma Rays
The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory is designed to
record air showers produced by cosmic rays and gamma rays between 100 GeV and
100 TeV. Because of its large field of view and high livetime, HAWC is
well-suited to measure gamma rays from extended sources, diffuse emission, and
transient sources. We describe the sensitivity of HAWC to emission from the
extended Cygnus region as well as other types of galactic diffuse emission;
searches for flares from gamma-ray bursts and active galactic nuclei; and the
first measurement of the Crab Nebula with HAWC-30
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The HAWC Gamma-Ray Observatory: Observations of Cosmic Rays
We describe measurements of GeV and TeV cosmic rays with the High-Altitude
Water Cherenkov Gamma-Ray Observatory, or HAWC. The measurements include the
observation of the shadow of the moon; the observation of small-scale and
large-scale angular clustering of the TeV cosmic rays; the prospects for
measurement of transient solar events with HAWC; and the observation of Forbush
decreases with the HAWC engineering array and HAWC-30
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Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory
The Crab Nebula is the brightest TeV gamma-ray source in the sky and has been used for the past 25 years as a reference source in TeV astronomy, for calibration and verification of new TeV instruments. The High Altitude Water Cherenkov Observatory (HAWC), completed in early 2015, has been used to observe the Crab Nebula at high significance across nearly the full spectrum of energies to which HAWC is sensitive. HAWC is unique for its wide field of view, nearly 2 sr at any instant, and its high-energy reach, up to 100 TeV. HAWC's sensitivity improves with the gamma-ray energy. Above ∼1 TeV the sensitivity is driven by the best background rejection and angular resolution ever achieved for a wide-field ground array. We present a time-integrated analysis of the Crab using 507 live days of HAWC data from 2014 November to 2016 June. The spectrum of the Crab is fit to a function of the form φ(E)= φ0(E/E0)-α-β In(E/E0). The data is well fitted with values of α = 2.63 ±0.03, β = 0.15 ±0.03, and log10(φ0cm2s TeV)=-12.60±0.02 when E 0 is fixed at 7 TeV and the fit applies between 1 and 37 TeV. Study of the systematic errors in this HAWC measurement is discussed and estimated to be ±50% in the photon flux between 1 and 37 TeV. Confirmation of the Crab flux serves to establish the HAWC instrument's sensitivity for surveys of the sky. The HAWC all-sky survey will be the deepest survey of the northern sky ever conducted in the multi-TeV band
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The HAWC Gamma-Ray Observatory: Design, Calibration, and Operation
The High-Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is under
construction 4100 meters above sea level at Sierra Negra, Mexico. We describe
the design and cabling of the detector, the characterization of the
photomultipliers, and the timing calibration system. We also outline a
next-generation detector based on the water Cherenkov technique
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The HAWC Gamma-Ray Observatory: Observations of Cosmic Rays
We describe measurements of GeV and TeV cosmic rays with the High-Altitude
Water Cherenkov Gamma-Ray Observatory, or HAWC. The measurements include the
observation of the shadow of the moon; the observation of small-scale and
large-scale angular clustering of the TeV cosmic rays; the prospects for
measurement of transient solar events with HAWC; and the observation of Forbush
decreases with the HAWC engineering array and HAWC-30