A Chandra X-ray Observation of the Binary Millisecond Pulsar PSR J1023+0038

TL;DR

This study uses Chandra X-ray observations to analyze the binary millisecond pulsar J1023+0038, revealing orbital variability, intrabinary shock characteristics, and spectral components, advancing understanding of pulsar wind interactions.

Contribution

It provides detailed X-ray variability, spectral analysis, and insights into the intrabinary shock geometry and pulsar wind properties of PSR J1023+0038.

Findings

Orbital X-ray flux varies significantly with eclipse features.

The intrabinary shock is near the companion star's surface.

No extended pulsar wind nebula detected down to luminosity limits.

Abstract

We present a Chandra X-ray Observatory ACIS-S variability, spectroscopy, and imaging study of the peculiar binary containing the millisecond pulsar J1023+0038. The X-ray emission from the system exhibits highly significant (12.5 sigma) large-amplitude (factor of 2-3) orbital variability over the five consecutive orbits covered by the observation, with a pronounced decline in the flux at all energies at superior conjunction. This can be naturally explained by a partial geometric occultation by the secondary star of an X-ray--emitting intrabinary shock, produced by the interaction of outflows from the two stars. The depth and duration of the eclipse imply that the intrabinary shock is localized near or at the surface of the companion star and close to the inner Lagrangian point. The energetics of the shock favor a magnetically dominated pulsar wind that is focused into the orbital plane, requiring close alignment of the pulsar spin and orbital angular momentum axes. The X-ray spectrum consists of a dominant non-thermal component and at least one thermal component, likely originating from the heated pulsar polar caps, although a portion of this emission may be from an optically-thin "corona". We find no evidence for extended emission due to a pulsar wind nebula or bow shock down to a limiting luminosity of L_X<3.6x10^29 ergs s^-1 (0.3-8 keV), <7x10^-6 of the pulsar spin-down luminosity, for a distance of 1.3 kpc and an assumed power-law spectrum with photon index Gamma=1.5.