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XTE J1856+053 observed by Swift/BAT

ATEL # 1093; H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team
on 1 Jun 2007; 13:54 UT
Password Certification: Hans A. Krimm (

Subjects: X-ray, Binaries, Black Holes, Transients

Swift/BAT reports a detection of the X-ray transient source XTE J1856+053. This source was seen in the 15-50 keV band in three separate pointings on May 28 and 30, 2007, with times and count rates:

MJD 54248 17:04:39 (1696 sec): 0.010 +/- 0.002 cts/sec/cm^2 (40 mCrab)
MJD 54250 19:05:03 (1312 sec): 0.016 +/- 0.003 cts/sec/cm^2 (70 mCrab)
MJD 54250 20:52:55 (840 sec): 0.013 +/- 0.002 cts/sec/cm^2 (55 mCrab)
MJD 54250 22:17:59 (1608 sec): 0.010 +/- 0.002 cts/sec/cm^2 (45 mCrab)

Although this source was not in the catalog for the Swift/BAT Hard X-ray Transient Monitor, we have examined archived sky images and see that the source has been detectable in daily averages since May 22, 2007 and that it also had a smaller hard X-ray outburst (reaching ~15 mCrab) from approximately Feb. 22- March 1, 2007, which was just before the outburst reported in the RXTE All-Sky Monitor (ASM) as beginning on Feb. 28, 2007 (ATEL #1024). The RXTE/ASM light curve ( ) shows a decline in flux to background levels by early May. The relative timing of the earlier BAT and ASM detections suggests that the source spectrum underwent a "pivot" from low-hard (detectable in BAT, but not ASM) to high-soft around March 1 and has now returned to the hard state. The current hard X-ray activity could presage renewed activity in the 2-10 keV band.

Swift/BAT Hard X-ray transient monitor observations of XTE J1856+053

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R. E. Rutledge , Editor
ATEL Mirror v1.0 Updates