A study of GeV gamma-ray emission towards supernova remnant G51.26+0.11 and its molecular environment

Abstract

We reanalyze the Fermi-LAT GeV γ-ray emission in the region of supernova remnant (SNR) G51.26+0.11 and investigate its interstellar molecular environment with the CO-line data. At GeV energies, based on 13.2 years of Fermi-LAT data, the extended γ-ray emission observed in this region is resolved into a uniform-disk source (‘Src A’) with a significance of 19.5σ and a point source (4FGL J1924.3+1628) with a significance of 4.2σ in 0.2–500 GeV. With an angular radius of ∼ 0.17○, ‘Src A’ overlaps with SNR G51.26+0.11 significantly in the line of sight. On the other hand, the morphological coincidence between the SNR and the ∼+54 km s−1 molecular clouds (MCs) together with the asymmetric or broad 12CO line profiles near the SNR boundary provides evidence for the very likely SNR-MC interaction. The SNR-MC interaction and the H I absorption features indicate that SNR G51.26+0.11 is located at a kinematic distance of 6.2 ± 0.5 kpc. Combined with the results from the multi-wavelength analysis, the γ-ray emission of the SNR (‘Src A’) can be naturally explained by a hadronic model with a soft power-law proton spectrum of index ∼ 2.25.

Cosmic Ray Processes in Galactic Ecosystems

“…However SNe with such a dense CSM that can be detected in γ-rays may not be common [123]. The high-energy emission from many SNRs is often instead attributed to the interactions of escaping CRs with nearby molecular clouds (e.g., [124][125][126][127][128][129]). Observations of SNR shells at other wavelengths are more informative.…”

“…Sometimes referred to as active molecular clouds, they are natural laboratories to investigate CR acceleration, propagation, and the feedback impacts CRs can deliver into the dense phases of the ISM. γrays provide information about CR interactions in molecular clouds near SNRs at energies above a GeV [124][125][126][127][128][129] (for early pre-Fermi era propositions and reviews, see [306,339]). The 6.4 keV neutral iron Kα line also traces MeV CRs in molecular clouds [340], as demonstrated by X-ray studies of known molecular clouds around SNRs [341][342][343][344][345][346][347].…”