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Swift/BAT Detects an Outburst from XTE J1901+014

ATEL # 2375; H. A. Krimm (CRESST/GSFC/USRA), P. Romano, S. Vercellone (INAF-IASF Palermo), S. D. Barthelmy (GSFC), W. Baumgartner (CRESST/GSFC/UMBC), J. Cummings (CRESST/GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. B. Markwardt (CRESST/GSFC/UMD), D. Palmer (LANL), T. Sakamoto (CRESTT/GSFC/UMBC), G. Skinner (CRESST/GSFC/UMD), M. Stamatikos (OSU/GSFC), J. Tueller (GSFC), T. Ukwatta (GSFC/GWU)
on 8 Jan 2010; 15:15 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Hans A. Krimm (

Subjects: X-ray, Request for Observations, Binaries, Black Holes, Neutron Stars, Transients

At 00:58:50.58 UT on 2010-Jan-08 (MJD 55204), Swift/BAT triggered on a rapid outburst from XTE J1901+014. The trigger was a 128-second image trigger and detectable emission lasted from T-150 sec to at least T+250 sec, when the spacecraft moved away from the field due to a pre-planned slew. The time-averaged spectrum from T-137.5 to T+263.9 sec is best fit by a simple power-law model. The photon power law index of the time-averaged spectrum is 5.22 +- 0.51. The fluence in the 15-150 keV band is 1.5 +- 0.2 x 10-6 erg/cm2. This corresponds to 0.056 0.010 ct/s/cm2 or 250 mCrab in the 15-50 keV band. Due to an observing constraint (proximity to the sun), no Swift XRT or UVOT observations will be possible until 2010-Feb-16.

This is the second time Swift/BAT has triggered on XTE J1901+014. The first was on 2006-June-06 at 10:17:18.76 for a weaker flare. The time-averaged spectrum of the 2006 flare from T+0.0 to T+33.1 sec was best fit by a simple power-law model. The photon power law index of the time-averaged spectrum was 4.32 +- 1.94 and the fluence in the 15-150 keV band was 1.1 +- 0.7 x 10-7 erg/cm2. The flux in a 1984-second observation beginning at 10:17:18 averaged 0.068 0.048 ct/s/cm2 (31 mCrab, 15-50 keV).

XTE J1901+014 is normally barely detectable in the BAT hard X-ray transient monitor at ~2.5 mCrab. It has shown signs of increased, but variable, activity since about 2009-Dec-03.

This source was discovered in 2002 (Remillard and Smith, ATel #88) and is known for having rapid, intense variations in its X-ray flux (e.g. Smith et al, ATel #1268). The true nature of the source is still in question. Optical photometry of the field suggests a low mass companion and the source may be the first low-mass fast X-ray transient (Karasev, Lutovinov & Burenin, 2008, Astron. Lett., 34, 753). This recent trigger tells us that XTE J1901+014 has again become active, so further observations are encouraged.

Swift/BAT Hard X-ray Transient light curve for XTE J1901+014

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R. E. Rutledge , Editor
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