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D. M. Smith (U. C. Berkeley), W. A. Heindl (U. C. San Diego), T. E. Harrison (New Mexico State University), J. H. Swank, C. B. Markwardt (NASA/Goddard)
XTE J1739-302 has been seen in at least five very brief outbursts by the Rossi X-ray Timing Explorer. Although it is located only two degrees from the Galactic Center and has a high x-ray absorption column, a Chandra observation in quiescence shows that its counterpart is a bright, highly reddened star much closer than the Galactic bulge. A K-band spectrum of this star suggests that it is an O supergiant without emission lines from an equatorial wind. The x-ray spectrum in outburst is similar to that of x-ray pulsars, very hard below 20 keV and rolling off rapidly above that energy, and is unlike any spectrum produced by black-hole binaries. The spectrum in quiescence is similarly hard. Pulsations with a period shorter than 300 s have been ruled out in outburst for amplitudes greater than 2% at 99% confidence. A search for longer periods is still in progress.
The typical duration of the outbursts is constrained to be more than a few hours but less than a few days, making them significantly shorter than the outbursts of Be/NS binaries. We will discuss the status of observations of this system and possible interpretations of its nature. XTE J1739-302 resides squarely in the most heavily-observed part of the x-ray sky yet was not discovered until 1997 due to the brevity of its outbursts; it therefore seems plausible that many such systems wait to be discovered elsewhere in the Galaxy.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.