High-Resolution Simulations of LS 5039

TL;DR

This paper presents high-resolution relativistic hydrodynamics simulations of the LS 5039 system, revealing turbulence and fluctuations in the wind-collision region that could influence non-thermal emission, especially gamma-ray variability.

Contribution

The study provides the first high-resolution, multi-orbit simulation of LS 5039's wind interaction, highlighting turbulence effects and their potential impact on emission variability.

Findings

Detected high turbulence levels at the wind-collision region.

Observed strong fluctuations in dynamical quantities around apastron.

Identified variations in gamma-ray emission regions on short and orbital timescales.

Abstract

Context. We present an analysis of our high-resolution relativistic-hydrodynamics model of the stellar- and pulsar-wind interaction in the LS-5039 system. Aims. With our high-resolution simulation covering three orbital periods, we analyse the impact of turbulence with a particular focus on short-term and orbit-to-orbit variations. Methods. Our model uses a relativistic hydrodynamics description of the wind interaction in the LS-5039 system assuming a pulsar-wind driven scenario. The corresponding system of equations is solved using the finite-volume code Cronos. We compute statistical quantities, also relevant for particle acceleration in this system, from results of multiple consecutive timesteps. Results. In our simulation we find the previously observed shock structures related to the wind-collision region (WCR), including the pulsar-wind termination, being dynamically influenced by orbital motion. In our high-resolution simulation we find high turbulence levels following from instabilities driven at the WCR. These instabilities lead to strong fluctuations of several dynamical quantities especially around and after apastron. These fluctuations are expected to impact the particle transport and also especially the related emission of non-thermal radiation. As an important example, the region from which gamma-ray emission has been found to be boosted due to relativistic beaming in previous studies shows strong variations in size both on short and on orbital timescales. Conclusions. Using a large computational domain together with high spatial resolution allowed a detailed study of fluctuations in the stellar- and pulsar-wind interaction. The results indicate a possible influence on the non-thermal emission from this system, which will be analysed with dedicated simulations in a forthcoming publication.