Discovery and follow-up studies of the extended, off-plane, VHE gamma-ray source HESS J1507-622

TL;DR

This paper reports the discovery of a new extended VHE gamma-ray source, HESS J1507-622, located off the Galactic plane, and discusses its possible astrophysical origins based on multiwavelength observations.

Contribution

The paper presents the first detection and detailed analysis of HESS J1507-622, an off-plane gamma-ray source, expanding understanding of VHE sources and their potential origins.

Findings

Detected HESS J1507-622 with > 9 sigma significance

Measured a power-law spectrum with index 2.24

Estimated flux above 1 TeV as 1.5 x 10^{-12} cm^{-2} s^{-1}

Abstract

Context: The detection of gamma-rays in the very-high-energy (VHE) range (100 GeV-100 TeV) offers the possibility of studying the parent population of ultrarelativistic particles found in astrophysical sources, so it is useful for understanding the underlying astrophysical processes in nonthermal sources. Aim: The discovery of the VHE gamma-ray source HESS J1507-622 is reported and possibilities regarding its nature are investigated. Methods: The H.E.S.S. array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compared with previous instruments (~1% of the Crab flux in 25 hours observation time for a 5 sigma point-source detection) and has a large field of view (~5 deg in diameter). HESS J1507-622 was discovered within the ongoing H.E.S.S. survey of the inner Galaxy, and the source was also studied by means of dedicated multiwavelength observations. Results: A Galactic gamma-ray source, HESS J1507-622, located ~3.5 deg from the Galactic plane was detected with a statistical significance > 9 sigma. Its energy spectrum is well fitted by a power law with spectral index \Gamma = 2.24 +/- 0.16_{stat} +/- 0.20_{sys} and a flux above 1 TeV of (1.5 +/- 0.4_{stat} +/- 0.3_{sys}) X 10^{-12} cm^{-2} s^{-1}. Possible interpretations (considering both hadronic and leptonic models) of the VHE gamma-ray emission are discussed in the absence of an obvious counterpart.