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XTE J1739-302

ATel #182; D. M. Smith (UCSC), W. A. Heindl (UCSD), J. H. Swank (NASA/GSFC), T. E. Harrison (NMSU), I. Negueruela (Alicante)
on 27 Aug 2003; 19:00 UT
Distributed as an Instant Email Notice Transients
Credential Certification: David M. Smith (dsmith@ssl.berkeley.edu)

Subjects: Infra-Red, Optical, X-ray, Request for Observations, Binary

Referred to by ATel #: 184, 218, 338

XTE J1739-302, which has just been reported as in outburst by Sunyaev et al. (ATEL #181), was observed previously by Chandra, although the results have not yet been published. The accurate position is

RA = 17 39 11.1, DEC = -30 20 37.6

This is close to the INTEGRAL position, increasing the probability that the current outburst is from this source.

Outbursts of this object have always had durations with an upper limit of 3 to 5 days, and may be even shorter: thus followup observations should be made as quickly as possible.

The optical counterpart is in the USNO A2.0 catalog, as object 0525 28760590. It is also a 2MASS source. The USNO photometry and recent infrared and optical spectroscopy (still being analyzed) suggest that the counterpart is a highly reddened O star, probably a supergiant, and almost certainly in the foreground rather than being located in the Galactic bulge.

Previous observations of outbursts with RXTE (Smith et al. 1998, ApJL 501, L101 and two unpublished events) and ASCA (Sakano et al. 2002, ApJS 138, 19) suggest the possibility of a pulsation period of approximately 1500s, although the evidence is still tentative since no more than two consecutive cycles have been observed.