Evidence for proton acceleration and escape from the Puppis A SNR using Fermi-LAT observations

TL;DR

This study uses 14 years of Fermi-LAT gamma-ray data to investigate proton acceleration and escape in the Puppis A supernova remnant, revealing asymmetrical emission and evidence of hadronic processes.

Contribution

It provides the first detailed morphological and spectral analysis of Puppis A with Fermi-LAT, identifying regions of proton acceleration and escape.

Findings

Asymmetrical gamma-ray brightness in Puppis A correlates with X-ray observations.

Eastern side shows pion decay spectrum indicating proton acceleration.

Detection of nearby gamma-ray sources suggests particle escape from the remnant.

Abstract

Supernova remnants (SNRs) are the best candidates for galactic cosmic ray acceleration to relativistic energies via diffusive shock acceleration. The gamma-ray emission of SNRs can provide direct evidence of leptonic (inverse Compton and bremsstrahlung) and hadronic (proton-proton interaction and subsequently pion decay) processes. Puppis A is a ~ 4 kyr old SNR interacting with interstellar clouds which has been observed in a broad energy band, from radio to gamma-ray. We performed a morphological and spectral analysis of 14 years of observations with Fermi-LAT telescope in order to study its gamma-ray emission. We found a clear asymmetry in high-energy brightness between the eastern and western sides of the remnant, reminiscent to that observed in the X-ray emission. The eastern side, interacting with a molecular cloud, shows a spectrum which can be reproduced by a pion decay model. Moreover, we analyzed two gamma-ray sources located close to the remnant. The hardness of their spectra suggests that the gamma-ray emission can be due to particles escaping from the shock of Puppis A.