A Chandra X-Ray observation of the binary millisecond pulsar PSR J1023+0038
Number of pages
Faculty of Science (FNWI)
Anton Pannekoek Institute for Astronomy (API)
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 (12.5σ) large-amplitude
(factor of two to three) 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 3.6 × 1029 erg s-1 (0.3-8 keV), 7 ×
10-6 of the pulsar spin-down luminosity, for a distance of 1.3 kpc and an assumed power-law spectrum with photon index Γ =
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