Journal Article

Anisotropic inverse Compton scattering of photons from the circumstellar disc in PSR B1259–63<sup>⋆</sup>

B. van Soelen, P. J. Meintjes, A. Odendaal and L. J. Townsend

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 426, issue 4, pages 3135-3147
Published in print November 2012 | ISSN: 0035-8711
Published online November 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21870.x
Anisotropic inverse Compton scattering of photons from the circumstellar disc in PSR B1259–63⋆

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Abstract

The gamma-ray binary system PSR B1259−63/LS 2883 consists of a 48 ms pulsar orbiting a Be star. The system is particularly interesting because it is the only gamma-ray binary system where the nature of the compact object is known. The non-thermal radiation from the system is powered by the spin-down luminosity of the pulsar and the unpulsed radiation originates from the stand-off shock front which forms between the pulsar and stellar wind. The Be star/optical companion in the system produces an excess infrared (IR) flux from the associated circumstellar disc. This IR excess provides an additional photon source for inverse Compton scattering. We discuss the effects of the IR excess near periastron, for anisotropic inverse Compton scattering and associated gamma-ray production. We determine the IR excess from the circumstellar disc using a modified version of a curve of growth method, which takes into account the changing optical depth through the circumstellar disc during the orbit. The model is constrained using archive data and additional mid-IR observations obtained with the Very Large Telescope (VLT) during 2011 January. The inverse Compton scattering rate was calculated for three orientations of the circumstellar disc. The predicted gamma-ray light curves show that the disc contribution is a maximum around periastron and not around the disc crossing epoch. This is a result of the disc being brightest near the stellar surface. Additional spectroscopic and near-IR observations were obtained of the system and these are discussed in relation to the possibility of shock heating during the disc crossing epoch.

Keywords: radiation mechanisms: non-thermal; pulsars: individual: PSR B1259−63; X-rays: binaries

Journal Article.  10067 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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