Fermi Large Area Telescope Observations of the Monoceros Loop Supernova Remnant

TL;DR

This paper analyzes Fermi LAT gamma-ray data of the Monoceros Loop SNR, revealing extended emission correlated with the SNR and nearby molecular cloud, with spectra favoring a curved shape and suggesting hadronic interactions as the emission origin.

Contribution

First detailed gamma-ray analysis of the Monoceros SNR showing spatial and spectral characteristics, supporting hadronic origin of the emission.

Findings

Gamma-ray emission is spatially extended and correlated with the SNR.

Spectra are better fit by a curved shape than a simple power law.

Gamma-ray luminosities are approximately 4 x 10^{34} erg/s for the SNR and 3 x 10^{34} erg/s for the Rosette Nebula.

Abstract

We present an analysis of the gamma-ray measurements by the Large Area Telescope onboard the \textit{Fermi Gamma-ray Space Telescope} in the region of the supernova remnant~(SNR) Monoceros Loop~(G205.5$+$0.5). The brightest gamma-ray peak is spatially correlated with the Rosette Nebula, which is a molecular cloud complex adjacent to the southeast edge of the SNR. After subtraction of this emission by spatial modeling, the gamma-ray emission from the SNR emerges, which is extended and fit by a Gaussian spatial template. The gamma-ray spectra are significantly better reproduced by a curved shape than a simple power law. The luminosities between 0.2--300~GeV are $\sim$~$4 \times 10^{34}$~erg~s$^{-1}$ for the SNR and $\sim$~$3 \times 10^{34}$~erg~s$^{-1}$ for the Rosette Nebula, respectively. We argue that the gamma rays likely originate from the interactions of particles accelerated in the SNR. The decay of neutral pions produced in nucleon-nucleon interactions of accelerated hadrons with interstellar gas provides a reasonable explanation for the gamma-ray emission of both the Rosette Nebula and the Monoceros SNR.