Revisiting Gamma-Ray Emission of the Supernova Remnant RCW 103

TL;DR

This study reanalyzes 15 years of Fermi-LAT gamma-ray data for SNR RCW 103, revealing a softer gamma-ray spectrum and associating emission with the remnant's southern limb interacting with a molecular cloud.

Contribution

It provides a refined gamma-ray spectral analysis of RCW 103, clarifies the source morphology, and supports a hadronic emission scenario linked to molecular cloud interaction.

Findings

Gamma-ray emission best described by a point source at the SNR's southern limb.

Photon index of the gamma-ray emission is approximately 2.31, softer than previous estimates.

Results support a hadronic origin involving protons with a spectral index around 2.4.

Abstract

We analyze more than 15 years of the \gr\ data, obtained with the Large Area Telescope (LAT) onboard {\it the Fermi Gamma-ray Space Telescope (Fermi)}, for the region of the young supernova remnant (SNR) RCW~103, since the nearby source 4FGL J1616.2$-$5054e, counterpart to HESS~J1616$-$518 and $\simeq$13\,arcmin away from the SNR, is determined to be extended in the more recent Fermi-LAT source catalog. Different templates for 4FGL J1616.2$-$5054e and RCW~103 are tested, and we find that a point source with a power-law (PL) spectrum at the southern limb of the SNR best describes the detected gamma-ray emission. The photon index of the PL emission is $\Gamma\simeq 2.31$(or $\alpha\simeq 2.4$ in a Log-Parabola model) , softer than the previously reported $\Gamma\simeq 2.0$ when the counterpart to HESS~J1616$-$518 was considered to be a point source (which likely caused mis-identification of extended emission at RCW~103). In order to produce the \gr\ emission in a hadronic scenario, we estimate that protons with an index$\sim$2.4 PL energy distribution are needed. These results fit with those from multi-wavelength observations that have indicated the remnant at the southern limb is interacting with a molecular cloud.