Fermi-LAT Observations and A Broadband Study of Supernova Remnant CTB 109

TL;DR

This study reports the detection of gamma-ray emission from supernova remnant CTB 109 using Fermi-LAT data, and models its broadband emission considering both leptonic and hadronic processes, constrained by thermal X-ray observations.

Contribution

It introduces a comprehensive broadband modeling approach that includes thermal X-ray emission, providing new constraints on the origin of gamma-ray emission in SNR CTB 109.

Findings

Gamma-ray emission coincides with CTB 109.

Both leptonic and hadronic models can fit the data.

An intermediate model with mixed electron and ion contributions best fits observations.

Abstract

CTB 109 (G109.1-1.0) is a Galactic supernova remnant (SNR) with a hemispherical shell morphology in X-rays and in the radio band. In this work we report the detection of {\gamma}-ray emission coincident with CTB 109, using 37 months of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. We study the broadband characteristics of the remnant using a model that includes hydrodynamics, efficient cosmic ray acceleration, nonthermal emission and a self-consistent calculation of the X-ray thermal emission. We find that the observations can be successfully fit with two distinct parameter sets, one where the {\gamma}-ray emission is produced primarily by leptons accelerated at the SNR forward shock and the other where {\gamma}-rays produced by forward shock accelerated cosmic-ray ions dominate the high-energy emission. Consideration of thermal X-ray emission introduces a novel element to the broadband fitting process, and while it does not rule out either the leptonic or the hadronic scenarios, it constrains the parameter sets required by the model to fit the observations. Moreover, the model which best fits the thermal and nonthermal emission observations is an intermediate case, where both radiation from accelerated electrons and hadrons contribute almost equally to the {\gamma}-ray flux observed.