Constraining leptonic and hadronic γ-ray emission from HESS J1825−137 and its environment

Abstract

We present a broadband spectral analysis of the γ-ray emission from the pulsar wind nebula HESS J1825−137, combining observations from Fermi-LAT, H.E.S.S., HAWC, and VERITAS across the ∼0.1 GeV–160 TeV energy range. The spectral energy distribution is modelled under purely leptonic, purely hadronic, and lepto-hadronic scenarios using the Naima radiative framework with Markov Chain Monte Carlo parameter estimation. Model comparison via the Bayesian Information Criterion reveals that the baseline GeV–TeV data favour a purely leptonic interpretation, while the inclusion of simulated CTAO observations or LHAASO ultra-high-energy measurements shifts the preference toward models incorporating a hadronic component (ΔBIC = −28.87 and −7.89, respectively). The inferred electron energy budget for the baseline GeV–TeV dataset, We = 4.25 × 1048 erg, is consistent with previous estimates reported in the literature. The proton energy budget, Wp ≈ 2.5 × 1048 erg, is energetically compatible with pp interactions in the dense molecular environment adjacent to the nebula. These results demonstrate that precise spectral measurements above ∼10 TeV, where Klein–Nishina suppression of inverse Compton emission creates a window for hadronic processes, are essential to establish the dominant emission mechanism in this source.