Physics & Astronomy


First Science Results from the HAWC Gamma-Ray Observatory

HAWCThe HAWC array viewed from the slope of Sierra Negra, July 2014. Credit: I. Taboada, Georgia Tech.

The High-Altitude Water Cherenkov Observatory (HAWC) is designed to study the sky in TeV gamma rays and observe the most energetic objects in the known universe. This week the collaboration published its first science result: a precise measurement of the anisotropy of Galactic cosmic rays above 1 TeV. The study was lead by members of HAWC from the University of Wisconsin-Madison and the University of Rochester.

Relative intensity of the cosmic-ray flux after the elimination of the large-scale structure. Image: HAWC Collaboration
Celestial coordinates of the small-scale cosmic-ray hot spots observed by HAWC. From: HAWC Colloration.

HAWC is a water-Cherenkov array designed to observe the extensive air showers produced by TeV cosmic rays and gamma rays. Located 4,100 m above sea level in Sierra Negra, Mexico, the completed observatory will comprise 300 water Cherenkov tanks, each 4.5 m tall and 7 m in diameter and containing 200,000 L of purified water.

Between the start of operations in June 2013 and February 2014, the partially-deployed HAWC detector recorded close to 50 billion cosmic rays and gamma rays. With these high statistics, Daniel Fiorino and Stefan Westerhoff of UW-Madison and Segev BenZvi of the University of Rochester were able to measure a significant small-scale anisotropy in the arrival directions of cosmic rays in the TeV region. The results, presented by the HAWC Collaboration in a paper accepted for publication in The Astrophysical Journal, exhibit three regions of significantly enhanced flux, in agreement with previous measurements in the Northern Hemisphere.

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