High-resolution simulations of non-thermal emission from LS 5039

¹ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstr. 25, 6020 Innsbruck, Austria
² Universität Innsbruck, Institut für Informatik, Technikerstr. 21a, 6020 Innsbruck, Austria

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 1 August 2025
Accepted: 20 December 2025

Abstract

Context. In a previous study, we investigated the relativistic wind dynamics in the LS 5039 system. In this work, we analyse energetic-particle transport within this modelling context, where we simulate the high-energy particle distribution and ensuing emission of non-thermal radiation.

Aims. From these high-resolution simulations covering three full orbits, we compute the non-thermal emission from this system and compare it to corresponding observations.

Methods. We modelled the LS 5039 system assuming a wind-driven scenario. Our numerical model uses a joint simulation of the dynamical wind interaction together with the transport of energetic leptons from the shocked pulsar wind. We computed the nonthermal emission from this system in a post-processing step from the resulting distribution of energetic leptons. In this computation, we took into account the synchrotron and inverse Compton emission, relativistic beaming, and γγ-absorption in the stellar radiation field.

Results. We investigated the dynamical variation of the energetic particle spectra on both orbital and on short timescales. From our simulation of three full orbits, we were also able to investigate the orbit-to-orbit variability. Our model successfully reproduces many of the spectral features of LS 5039. We also find a better correspondence between our predicted orbital light curves and the corresponding observations in soft x-rays, low-energy, and high-energy gamma rays than in our previous modelling efforts.

Conclusions. We find that our high-resolution and large-scale simulations can successfully capture the relevant parts of the windcollision region that are related to particle acceleration and emission of non-thermal radiation. The quality of the fit strengthens the wind-driven assumption underlying our model. Desirable extensions for the future include a dynamical magnetic-field model for the synchrotron regime, a revision of our injection parameters, and a consideration of an additional hadronic component that could explain recent observations in the 100 TeV regime.