3D Relativistic MHD simulations of the gamma-ray binaries

TL;DR

This paper uses 3D relativistic MHD simulations to study the complex, orbit-dependent interactions between stellar and pulsar winds in gamma-ray binaries, explaining observed phase-dependent emission features.

Contribution

It introduces detailed 3D relativistic MHD simulations to model wind interactions and their impact on observable emission in gamma-ray binaries, highlighting the importance of geometrical factors.

Findings

Intrinsic morphologies vary with orbital phase.

Unshocked pulsar wind region can change significantly.

Modeled light curves match observed phase-dependent data.

Abstract

In gamma-ray binaries neutron star is orbiting a companion that produces a strong stellar wind. We demonstrate that observed properties of "stellar wind"-"pulsar wind" interaction depend both on the overall wind thrust ratio, as well as more subtle geometrical factors: the relative direction of the pulsar's spin, the plane of the orbit, the direction of motion, and the instantaneous line of sight. Using fully 3D relativistic magnetohydrodynamical simulations we find that the resulting intrinsic morphologies can be significantly orbital phase-dependent: a given system may change from tailward-open to tailward-closed shapes. As a result, the region of unshocked pulsar wind can change by an order of magnitude over a quarter of the orbit. We calculate radiation maps and synthetic light curves for synchrotron (X-ray) and Inverse-Compton emission (GeV-TeV), taking into account $\gamma-\gamma$ absorption. Our modeled light curves are in agreement with the phase-dependent observed light curves of LS5039.