Global Kinetic Modeling of the Intrabinary Shock in Spider Pulsars

TL;DR

This paper uses kinetic simulations to model the intrabinary shock in spider pulsars, revealing efficient particle acceleration and producing spectra and lightcurves consistent with X-ray observations.

Contribution

It presents the first global kinetic particle-in-cell simulations of the intrabinary shock in spider pulsars, demonstrating shock-driven reconnection and realistic emission features.

Findings

Particles are efficiently accelerated via shock reconnection.

Synchrotron spectra are nearly flat, matching observations.

Lightcurves show double peaks due to Doppler boosting.

Abstract

Spider pulsars are compact binary systems composed of a millisecond pulsar and a low-mass companion. The relativistic magnetically-dominated pulsar wind impacts onto the companion, ablating it and slowly consuming its atmosphere. The interaction forms an intrabinary shock, a proposed site of particle acceleration. We perform global fully-kinetic particle-in-cell simulations of the intrabinary shock, assuming that the pulsar wind consists of plane-parallel stripes of alternating polarity and that the shock wraps around the companion. We find that particles are efficiently accelerated via shock-driven reconnection. We extract first-principles synchrotron spectra and lightcurves which are in good agreement with X-ray observations: (1) the synchrotron spectrum is nearly flat, $F_\nu\propto {\rm const}$; (2) when the pulsar spin axis is nearly aligned with the orbital angular momentum, the light curve displays two peaks, just before and after the pulsar eclipse (pulsar superior conjunction), separated in phase by $\sim 0.8\, {\rm rad}$; (3) the peak flux exceeds the one at inferior conjunction by a factor of ten. We demonstrate that the double-peaked signature in the lightcurve is due to Doppler boosting in the post-shock flow.