Smith, David M., Markwardt, Craig B., Swank, Jean H., Negueruela, Ignacio
Fast X-ray transients towards the Galactic bulge with the Rossi X-ray Timing Explorer
Monthly Notices of the Royal Astronomical Society. 2012, 422(3): 2661-2674. doi:10.1111/j.1365-2966.2012.20836.x
URI: http://hdl.handle.net/10045/33863
DOI: 10.1111/j.1365-2966.2012.20836.x
ISSN: 0035-8711 (Print)
Abstract: 
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
Royal Astronomical Society
info:eu-repo/semantics/article