Hadronic particle acceleration in the supernova remnant SN 1006 as traced by Fermi-LAT observations

TL;DR

This study uses 15 years of Fermi-LAT data to analyze gamma-ray emission from SN 1006, revealing distinct spectral properties of its NE and SW limbs and supporting a hadronic acceleration model.

Contribution

It provides the first detailed morphological and spectral analysis of SN 1006's gamma-ray emission above 1 GeV, distinguishing between leptonic and hadronic processes in different regions.

Findings

Detection of NE limb at 6σ and SW limb at 5.5σ significance.

NE limb has a hard spectral index of 1.7, SW has a steeper index of 2.2.

Evidence of proton-proton interactions in the SW due to dense medium.

Abstract

The supernova remnant SN 1006 is a source of high-energy particles detected at radio, X-rays, and tera-electronvolt gamma rays. It was also announced as a source of gamma rays by Fermi-LAT but only the north-east (NE) limb was detected at more than $5\sigma$ significance level. Using 15 years of Fermi-LAT observation and a thorough morphological analysis above 1 GeV, we report the detection of the NE rim at the $6\sigma$ level and the south-west (SW) rim at the $5.5\sigma$ level using radio templates from the GLEAM survey. The spectral analysis performed between 100 MeV and 1 TeV allows the detection of a hard spectral index for the NE limb of $1.7 \pm 0.1 \pm 0.1$ while the emission detected in the SW is well reproduced with a steeper spectral index of $2.2 \pm 0.1 \pm 0.1$. A marginal detection (~$3\sigma$) of emission coincident with the bright north-west (NW) H$\alpha$ filament is also described with a similar spectral index of ~2.1. We successfully characterized the non-thermal multi-wavelength emission of the NE and SW limbs with a model in which inverse-Compton emission dominates in the NE while proton-proton interactions becomes significant in the SW due to the enhanced density of the medium.