Gamma-Ray Emission from LS 5039: A 30-500 GeV Excess and Phase-Resolved Broadband Spectral Modeling
Abstract
LS~5039 is a well-studied γ-ray binary exhibiting strong orbital modulation from GeV to TeV energies. We present a phase-resolved analysis of 17.3~yr of \textit{Fermi}-LAT observations and identify an additional γ-ray excess in the ∼30--$500$~GeV at a significance of ∼7.9σ. The phase-resolved spectra show pronounced orbital dependence above ∼10~GeV, with the inferior-conjunction more complex than the superior-conjunction. To investigate the broadband spectral energy distribution, we combine the \textit{Fermi}-LAT spectra with published H.E.S.S.\ and HAWC measurements and compare purely leptonic and lepto-hadronic models using the Bayesian information criterion. In both intervals, relativistic-Maxwellian and magnetospheric components dominate below ∼10~GeV, while shock-accelerated electrons account for much of the GeV--TeV continuum. The purely leptonic fits leave residuals at $30−−500$~GeV and underpredict the HAWC measurements above ∼100~TeV. In the local one-zone intrabinary shock apex model, synchrotron cooling and Klein-Nishina suppression make the ultra-high-energy emission difficult to reproduce, although more complex leptonic scenarios remain possible. Adding a phenomenological proton component improves the broadband description, with stronger relative support during superior-conjunction than inferior-conjunction. However, the proton parameters remain weakly constrained and the fast-escape hadronic interpretation is energetically challenging, so a hadronic origin is not uniquely established. Future high-sensitivity, phase-resolved observations at multi-TeV and ultra-high energies will be required to test this interpretation.
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BibTeX
@misc{zhao2026gammaray,
title = {{Gamma-Ray Emission from LS 5039: A 30-500 GeV Excess and Phase-Resolved Broadband Spectral Modeling}},
author = {Xiaozhen Zhao and Jiandong Zhang and Pengfei Zhang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.41739},
eprint = {2610.41739},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.41739},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Gamma-Ray Emission from LS 5039: A 30-500 GeV Excess and Phase-Resolved Broadband Spectral Modeling
AU - Xiaozhen Zhao
AU - Jiandong Zhang
AU - Pengfei Zhang
PY - 2026
DA - 2026/10/30
PB - arXiv
DO - 10.48550/arxiv.2610.41739
UR - https://arxiv.org/abs/2610.41739
AB - LS~5039 is a well-studied γ-ray binary exhibiting strong orbital modulation from GeV to TeV energies. We present a phase-resolved analysis of 17.3~yr of \textit{Fermi}-LAT observations and identify an additional γ-ray excess in the ∼30--$500$~GeV at a significance of ∼7.9σ. The phase-resolved spectra show pronounced orbital dependence above ∼10~GeV, with the inferior-conjunction more complex than the superior-conjunction. To investigate the broadband spectral energy distribution, we combine the \textit{Fermi}-LAT spectra with published H.E.S.S.\ and HAWC measurements and compare purely leptonic and lepto-hadronic models using the Bayesian information criterion. In both intervals, relativistic-Maxwellian and magnetospheric components dominate below ∼10~GeV, while shock-accelerated electrons account for much of the GeV--TeV continuum. The purely leptonic fits leave residuals at $30−−500$~GeV and underpredict the HAWC measurements above ∼100~TeV. In the local one-zone intrabinary shock apex model, synchrotron cooling and Klein-Nishina suppression make the ultra-high-energy emission difficult to reproduce, although more complex leptonic scenarios remain possible. Adding a phenomenological proton component improves the broadband description, with stronger relative support during superior-conjunction than inferior-conjunction. However, the proton parameters remain weakly constrained and the fast-escape hadronic interpretation is energetically challenging, so a hadronic origin is not uniquely established. Future high-sensitivity, phase-resolved observations at multi-TeV and ultra-high energies will be required to test this interpretation.
ER -