Phase-resolved hard X-ray emission of the high-mass binary LS 5039: a spectral hardening above 50 keV detected with INTEGRAL

TL;DR

This study analyzes phase-resolved multi-instrument spectra of LS 5039, revealing a spectral hardening above 50 keV that suggests complex particle acceleration processes in this high-mass gamma-ray binary.

Contribution

It provides the first phase-resolved spectral analysis combining X-ray and gamma-ray data, identifying a spectral break indicative of particle acceleration mechanisms.

Findings

Spectral hardening above 50 keV detected

Phase-resolved spectra reveal spectral break in both binary phases

Indicates possible interaction between stellar wind and relativistic outflow

Abstract

Aims: LS 5039 is an enigmatic high-mass gamma-ray binary which hosts a powerful O6.5V companion, but the nature of the compact object is still to be established using multi-wavelength observations. Methods: We analyzed phase-resolved multi-instrument spectra of nonthermal emission from LS 5039 in order to produce reliable spectral models, which can be further employed to select between various scenarios and theoretical models of the binary. Results: The combined phase-resolved hard X-ray and MeV-range gamma-ray spectra obtained with XMM-Newton, Suzaku, NuSTAR, INTEGRAL, and COMPTEL indicate a meaningful spectral hardening above 50~keV. The spectral break observed in both major phases of the binary may indicate the presence of a hardening in the spectrum of accelerated leptons which could originate from the interaction of wind from the O6.5V companion star with the relativistic outflow from a yet unidentified compact object.