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ATEL # 1709; C. B. Markwardt (CRESST/U.Md./NASA/GSFC), H. Krimm (CRESST/USRA/NASA/GSFC), R. Wijnands (U. Amsterdam), J. H. Swank (NASA/GSFC)
on 9 Sep 2008; 6:58 UT
Password Certification: Craig B. Markwardt (email@example.com)
Subjects: X-ray, Gamma Ray, Request for Observations, Binaries, Black Holes, Neutron Stars, Transients
Referred to by ATEL #: 1711, 1714
In Feb-March 2004, scans of the galactic bulge region by RXTE PCA detected a new excess. At the time, position scans were done, with the resulting best fit position of RA, Dec = 264.4606, -37.6605 (J2000), with a position error radius of 4 arcmin (95% confidence). The outburst in 2004 lasted from approximately 2004-02-14 through 2004-03-23, with peak fluxes of 6 mCrab (2-10 keV). At the time, we designated the source XTE J1737-376. Little was known about the source at the time, and it was not reported publicly, although it appeared on the PCA bulge scan web page.
A new outburst has been detected from this source. Starting 2008-09-02, the PCA flux began rising, from ~2 mCrab to about 12 mCrab on 2008-09-06 (2-10 keV). Since the previous outburst in 2004, the upper limits have been in the 0.5-2 mCrab range (2-10 keV).
The Swift/Burst Alert Telescope (BAT) transient monitor also detected an excess from the same part of the sky. Starting on 2008-09-02, the BAT 15-50 keV flux rose from undetectability to a count rate of (0.003 +/- 0.001) counts/sec/cm2 (~10 mCrab). The flux has remained roughly constant since that time. The best BAT position is RA, Dec= 264.528, -37.789 (J2000) with a 90% confidence error radius of 2.9 arc minutes.
A weak hard X-ray source was reported in the 3rd INTEGRAL catalog (Bird et al. 2007, ApJS, 170, 175), IGR J17379-3747, at position RA, Dec = 264.473, -37.783, with error radius 5.3 arcmin (90% confidence). The INTEGRAL catalog does not report whether the source is transient or persistent.
The BAT and INTEGRAL positions are consistent with each other. Also, the coincidence in time between BAT and PCA detections strongly suggests that this pair is the same source, although their positional overlap is somewhat marginal. Taking all the evidence together, we believe it is most likely all three of these detections are the same source, IGR J17379-3747 = XTE J1737-376.
RXTE and Swift follow-up observations are planned.
RXTE PCA scan light curve of XTE J1737-376