Journal Article

Fast X-ray transients towards the Galactic bulge with the <i>Rossi X-ray Timing Explorer</i>

D. M. Smith, C. B. Markwardt, J. H. Swank and I. Negueruela

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 422, issue 3, pages 2661-2674
Published in print May 2012 | ISSN: 0035-8711
Published online May 2012 | e-ISSN: 1365-2966 | DOI:
Fast X-ray transients towards the Galactic bulge with the Rossi X-ray Timing Explorer

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In X-ray binaries, rapid variability in X-ray flux of greater than an order of magnitude on time-scales of a day or less appears to be a signature of wind accretion from a supergiant companion. When the variability takes the form of rare, brief, bright outbursts with only faint emission between them, the systems are called supergiant fast X-ray transients (SFXTs). We present data from twice-weekly scans of the Galactic bulge by the Rossi X-ray Timing Explorer that allow us to compare the behaviour of known SFXTs and possible SFXT candidates with the persistently bright supergiant X-ray binary 4U 1700−377. We independently confirm the orbital periods reported by other groups for SFXTs SAX J1818.6−1703 and IGR J17544−2619. The new data do not independently reproduce the orbital period reported for XTE J1739−302, but slightly improve the significance of the original result when the data are combined. The bulge source XTE J1743−363 shows a combination of fast variability and a long-term decline in activity, the latter behaviour not being characteristic of supergiant X-ray binaries. A far-red spectrum of the companion suggests that it is a symbiotic neutron star binary rather than a high-mass binary, and the reddest known of this class: the spectral type is approximately M8 III.

Keywords: accretion, accretion discs; binaries: symbiotic; stars: neutron; supergiants; X-rays: binaries

Journal Article.  8001 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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