The supernova remnant W49B as seen with H.E.S.S. and Fermi-LAT

TL;DR

This study reports the detection and analysis of gamma-ray emission from supernova remnant W49B using H.E.S.S. and Fermi-LAT, revealing spectral features indicative of hadronic cosmic-ray acceleration.

Contribution

First combined VHE and HE gamma-ray spectral analysis of W49B, identifying spectral breaks consistent with neutral-pion decay, advancing understanding of cosmic-ray origins in SNR/MC systems.

Findings

Detection of gamma-ray emission from W49B at VHE and HE energies.

Identification of spectral breaks at ~304 MeV and ~8.4 GeV.

Spectral features suggest gamma-ray production via neutral-pion decay.

Abstract

The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). $\gamma$-ray observations of SNR/MC associations are a powerful tool to constrain the origin of Galactic cosmic-rays, as they can probe the acceleration of hadrons through their interaction with the surrounding medium and subsequent emission of non-thermal photons. The detection of a $\gamma$-ray source coincident with W49B at very high energies (VHE; E > 100 GeV) with the H.E.S.S. Cherenkov telescopes is reported together with a study of the source with 5 years of Fermi-LAT high energy $\gamma$-ray (0.06 - 300 GeV) data. The smoothly-connected combined source spectrum, measured from 60 MeV to multi-TeV energies, shows two significant spectral breaks at $304\pm20$ MeV and $8.4_{-2.5}^{+2.2}$ GeV, the latter being constrained by the joint fit from the two instruments. The detected spectral features are similar to those observed in several other SNR/MC associations and are found to be indicative of $\gamma$-ray emission produced through neutral-pion decay.