Abstract
HESSJ1825-137 is one of the most powerful and luminous TeV gamma-ray pulsar wind nebulae (PWN). To the south of HESSJ1825-137, 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 HESSJ1825-137, the progenitor SNR also associated with HESSJ1825-137, plus the gamma-ray binary system LS5039. It was found that the progenitor SNR of HESSJ1825-137 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 HESS1825-137, assuming fast diffusion perhaps including advection. LS5039 cannot meet the required energetics to be the source of particle acceleration. A combination of HESSJ1825-137 and LS5039 could be plausible sources.