An evaluation of CTools for H.E.S.S data analysis

Abstract

The present analysis of gamma-ray emissions is carried out through various detector/instrument-specific software frameworks. The structural analysis of gamma-ray sources in a H.E.S.S data set involves folding an initial source model with a spectra index-dependent point spread function to produce a model describing the expected emission of gamma-rays within the region of interest. Thus, when analysing a combination of closely separated sources, an analysis approach is needed in which the different spectral properties of each source is taken into account. The existing method for describing structural properties of gamma-ray sources within a H.E.S.S. data set involves fitting each source in the field of interest separately and ignoring any spillovers. This project proposes an analysis technique which simultaneously fits the spectraand morphologies of multiple gamma-ray emitters with different spatial andspectral shapes. The technique involves simultaneously folding a source model foreach individual source in the region of interest with the respective point spread function to produce a combined model of all the sources of interest. Such ananalys is was carried out by utilising the CTools software package. The viability of using CTools as a means of analysis of H.E.S.S. data was evaluated by determining the sensitivity of the software and how spectral and morphological results compare with that of already studied gamma-ray emitters. A simulated CTA data set served as the application domain of the former and historical H.E.S.S. data of N 157B and 30 Dor C for the latter. The results from the spectral and morphological analyses were further compared and shown in conjunction with published findings. It was determined that CTools is able to detect a cut-off in a CTA spectrum between 0.14 TeV and 12 TeV and can additionally distinguish confused sources, where source contamination is a factor, up to an offset of 0.05o. Ultimately, 30 DorC was found to have a radial disk-like morphology described by a power-law spectrum with a spectral index of -2.57±0.15 and a differential flux of (3.09±0.51)×10−19ph.cm−2.s−1.MeV−1. N 157B was determined to be a point source with a power-law spectrum with an associated spectral index of -2.67±0.07 and a differential flux of (1.14±0.51)×10−18ph.cm−2.s−1.MeV−1within the H.E.S.S. energy range. This derived spectrum was combined with Fermi-LAT data to model the break in the non-thermal emission of N 157B