Explaining the extended GeV gamma-ray emission adjacent to HESS J1825-137

TL;DR

This paper investigates the origin of GeV gamma-ray emission near HESS J1825-137, analyzing various astrophysical sources and models to determine the most plausible particle acceleration mechanisms.

Contribution

It provides a comprehensive analysis of potential sources for the GeV emission, ruling out some and suggesting a combined origin involving the PWN and LS 5039.

Findings

Progenitor SNR lacks sufficient energy to explain the GeV emission.

GeV-ABC may reflect an earlier phase of the PWN's evolution.

LS 5039 alone cannot account for the observed energetics.

Abstract

HESS J1825-137 is one of the most powerful and luminous TeV gamma-ray pulsar wind nebulae (PWN). To the south of HESS J1825-137, Fermi-LAT observation revealed a new region of GeV gamma-ray emission with three apparent peaks (termed here, GeV-ABC). This study presents interstellar medium (ISM) data and spectral energy distribution (SED) modelling towards the GeV emission to understand the underlying particle acceleration. We considered several particle accelerator scenarios - the PWN associated with HESS J1825-137, the progenitor SNR also associated with HESS J1825-137, plus the gamma-ray binary system LS\,5039. It was found that the progenitor SNR of HESS J1825-137 has insufficient energetics to account for all GeV emission. GeV-ABC may be a reflection of an earlier epoch in the history of the PWN associated with HESS\,1825-137, assuming fast diffusion perhaps including advection. LS\,5039 cannot meet the required energetics to be the source of particle acceleration. A combination of HESS J1825-137 and LS 5039 could be plausible sources.