The extended H.E.S.S. Galactic Plane survey: Discovering and identifying new sources of VHE γ-rays

Abstract

H.E.S.S. is an array of four imaging atmospheric-Cherenkov telescopes located in Namibia and designed to detect gamma rays in the very-high-energy (VHE; 0.1 < E < 100 TeV) domain. The full array has been in operation and observing the Galaxy since late 2003. The H.E.S.S. array’s large field-of-view, high sensitivity, and location in the southern hemisphere have made it well-suited for both systematic surveying and for deeply observing specific sources of interest. The efforts of the H.E.S.S. Galactic Plane Survey (GPS), the first comprehensive survey of the inner Galaxy (current l = 280 deg to 60 deg, b +/- 4 deg) at TeV energies, have contributed to the discovery of an unexpectedly large and diverse population of over 60 sources of VHE gamma rays. In this thesis, the latest dataset of the H.E.S.S. GPS is presented in detail, providing the most complete view of the Galaxy in the VHE gamma-ray regime to date. The resulting discoveries of four previously unknown VHE gamma-ray sources -- HESS J1708-443, HESS J1503-582, HESS J1832-084, and HESS J1848-018 -- are reported in particular, and their associations with astrophysical phenomena seen at lower energies are investigated with the aid of both dedicated and archival multi-wavelength data, in an attempt to reveal their physical nature. In addition, deep observations of the youngest Galactic supernova remnant (SNR) G1.9+0.3 are used to probe its VHE gamma-ray emission in light of theoretical predictions. Finally, the first study to correlate bright MeV–GeV gamma-ray sources with VHE gamma-ray sources is presented. Although the current population of VHE gamma-ray emitters is found to be dominated by pulsar wind nebulae (PWNe) and SNRs, nearly a third still remain unidentified or confused, illustrating both the challenges and scientific potential that pervade Galactic TeV astronomy.