The high-energy gamma-ray detection of G73.9+0.9, a supernova remnant interacting with a molecular cloud

TL;DR

This study confirms high-energy gamma-ray emission from SNR G73.9+0.9, indicating interaction with a molecular cloud and providing insights into the particle acceleration and magnetic field in the remnant.

Contribution

The paper presents the first detailed analysis of gamma-ray emission from G73.9+0.9, confirming its origin from hadronic interactions and estimating the magnetic field strength in the remnant.

Findings

Gamma-ray emission detected at 12σ significance.

Gamma-ray spectrum shows a peak at ~1 GeV with curvature.

Estimated magnetic field strength is ≥80 μG.

Abstract

We have analysed the Fermi LAT data on the SNR G73.9+0.9. We have confirmed a previous detection of high-energy gamma-rays from this source at a high significance of $\simeq 12\sigma$. The observed spectrum shows a significant curvature, peaking in $E F_E$ at $\sim$1 GeV. We have also calculated the flux upper limits in the mm-wavelength and X-ray ranges from Planck and XMM-Newton, respectively. We have inspected the intensity of the CO (1$\rightarrow $0) emission line and found a large peak at a velocity range corresponding to the previously estimated source distance of $\sim$4 kpc, which may indicate an association between a molecular cloud and the SNR. The gamma-ray emission appears due to interaction of accelerated particles within the SNR with the matter of the cloud. The most likely radiative process responsible for the gamma-ray emission is decay of neutral pions produced in ion-ion collisions. While a dominant leptonic origin of this emission can be ruled out, the relativistic electron population related to the observed radio flux will necessarily lead to a certain level of bremsstrahlung gamma-ray emission. Based on this broad-band modelling, we have developed a method to estimate the magnetic field, yielding $B\geq 80\,\mu$G at our best estimate of the molecular cloud density (or less at a lower density). G73.9+0.9 appears similar, though somewhat weaker, to other SNRs interacting with a local dense medium detected by the LAT.