A spectral analysis of the Crab nebula and other sources with HAWC

Abstract

The High Altitude Water Cherenkov observatory (HAWC) is an extensive air shower particle detection array designed to study cosmic gamma (γ) rays in the Very High Energy (VHE) regime (100 GeV to 100 TeV). One of the most thoroughly studied sources in this energy range is the Crab nebula, a pulsar wind nebula created by the aftermath of supernova 1054. The core of this analysis revolves around the determination of the differential flux spectrum of the Crab nebula using a process known as forward folding. Forward folding allows energy spectra to be fit without requiring a direct measurement of the primary energy of individual extensive air showers. The energy resolution of HAWC is very poor (on the order of 50% or more), and so this method is ideal for any spectral analysis carried out with HAWC data. The differential spectra are modeled as a power law with a normalization (Φ0), spectral index (γ), and a cutoff energy (Ec): dN/dE = Φ0(E/E0)γe−E/Ec . The normalization of the Crab nebula was found to be 1.03±0.091 0.083 stat ±0.19 sys)×10−12(TeV−1 cm−2 s −1 ) with an index of −2.54 ± 0.095 stat ± 0.27 sys and a cutoff of 91.0 ±174 59 stat with E0 =4.0 TeV. This method was also applied to 11 other sources, and the minimum detection significance required to constrain a spectrum was found to be between 10 and 14 σ.