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D. M. Smith (U. C. Santa Cruz), I. Negueruela (University of Alicante), W. A. Heindl (U. C. San Diego), C. B. Markwardt, J. H. Swank (NASA/GSFC)
Recently, there have been x-ray observing campaigns capable of monitoring the inner Galaxy frequently and over large areas of sky, notably those performed with the BeppoSAX wide-field camera, the INTEGRAL observatory, and the bulge scan campaign of the Rossi X-ray Timing Explorer (RXTE). These campaigns have begun to remove a long-standing observational bias against the discovery of transient sources with very short lifetimes. Two sources have recently been discovered, XTE J1739-302 and IGR J17544-2619/1RXS J175428.3-262035, which show outbursts with durations from about an hour to about a day, with no pulsations detected so far. The former has been observed in outburst by RXTE and ASCA, and has been shown, through a series of followup observations, to have a blue supergiant companion (O7.5-8Iaf) and to be a foreground object (distance on the order of 1.8 kpc) despite its position near the Galactic center. IGR J17544-2619, which has been observed in multiple short outbursts by INTEGRAL and RXTE, is very close to a USNO B1.0/2MASS counterpart (J. Rodriguez, ATEL #194) with magnitudes and colors very similar to the counterpart of XTE J1739-302, and is therefore probably a very similar system. These sources may be very common in the Galaxy, being discovered in the field of the Galactic bulge only because that's where we're looking. We will review the observations and discuss plans for followup of other RXTE fast transients which may be members of the same class.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.