Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B

TL;DR

This study analyzes Fermi-LAT gamma-ray data of supernova remnant W49B, revealing a bright gamma-ray source coinciding with the remnant, with spectral features consistent with hadronic or leptonic emission mechanisms.

Contribution

First detailed gamma-ray analysis of SNR W49B with spectral characterization and implications for particle acceleration mechanisms.

Findings

Detected a bright gamma-ray source coinciding with W49B

Spectrum steepens at higher energies in the 0.2-200 GeV range

Relativistic particle energy density estimated to be >10^4 eV/cm^3

Abstract

We present an analysis of the gamma-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a significance of 38 sigma is found to coincide with SNR W49B. The energy spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy range. There is no indication that the gamma-ray emission comes from a pulsar. Assuming that the SNR shell is the site of gamma-ray production, the observed spectrum can be explained either by the decay of neutral pi mesons produced through the proton-proton collisions or by electron bremsstrahlung. The calculated energy density of relativistic particles responsible for the LAT flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either gamma-ray production mechanism.