Performance of the HAWC Observatory and TeV Gamma-Ray Measurements of the Crab Nebula with Improved Extensive Air Shower Reconstruction Algorithms
arxiv(2024)
摘要
The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory located on the
side of the Sierra Negra volcano in Mexico, has been fully operational since
2015. The HAWC collaboration has recently significantly improved their
extensive-air-shower reconstruction algorithms, which has notably advanced the
observatory performance. The energy resolution for primary gamma rays with
energies below 1 TeV was improved by including a noise-suppression algorithm.
Corrections have also been made to systematic errors in direction fitting
related to the detector and shower plane inclinations,
𝒪(0.1^∘) biases in highly inclined showers, as well as
enhancements to the core reconstruction. The angular resolution for gamma rays
approaching the HAWC array from large zenith angles (> 37^∘) has
improved by a factor of four at the highest energies (> 70 TeV) as compared
to previous reconstructions. The inclusion of a lateral distribution function
fit to the extensive air shower footprint on the array to separate gamma-ray
primaries from cosmic-ray ones, based on the resulting χ^2 values,
improved the background rejection performance at all inclinations. At large
zenith angles, the improvement in significance is a factor of four compared to
previous HAWC publications. These enhancements have been verified by observing
the Crab Nebula, which is an overhead source for the HAWC Observatory. We show
that the sensitivity to Crab-like point sources (E^-2.63) with locations
overhead to 30^∘ zenith is comparable or less than 10% of the Crab
Nebula's flux between 2 and 50 TeV. Thanks to these improvements, HAWC can now
detect more sources, including the Galactic Center.
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