Ultra-high Energy Gamma-rays from Past Explosions in our Galaxy

TL;DR

This paper explains the origin of ultra-high energy gamma rays from specific galactic sources by proposing that past explosions injected shock-accelerated particles, leading to observed emissions without nearby pulsars or supernova remnants.

Contribution

It introduces a novel scenario where past explosions account for gamma-ray emissions in sources lacking nearby energetic objects.

Findings

Observed gamma-ray flux explained by secondary gamma rays from evolved particles

Past explosions can produce current gamma-ray emissions without nearby pulsars

Supports shock acceleration and secondary gamma-ray production as key mechanisms

Abstract

The discovery of the sources of ultra-high energy photons by High-Altitude Water Cerenkov Gamma ray Observatory and Large High Altitude Air Shower Observatory in our Galaxy has revolutionised the field of gamma ray astronomy in the last few years. These emissions are sometimes found in the vicinity of powerful pulsars or supernova remnants associated with giant molecular clouds. Inverse Compton emission by shock accelerated electrons emitted by pulsars and proton-proton interactions of shock accelerated protons emitted by supernova remnants with cold protons in molecular clouds are often identified as the causes of these emissions. In this paper we have selected two ultra-high energy photon sources LHAASO J2108+5157 and LHAASO J0341+5258 which are associated with giant molecular clouds, but no powerful pulsar or supernova remnant has been detected in their vicinity.We have proposed a scenario where shock accelerated electrons and protons are injected in the local environment of these sources from past explosions, which happened thousands of years ago. We show that the observed ultra-high energy photon flux can be explained with the secondary gamma rays produced by the time evolved relativistic electron and proton spectra.