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Swift/BAT Detects Increased Activity from the Accreting Pulsar GRO J1750-27

ATel #1376; H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), J. Cummings (CRESST/GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. Markwardt (CRESST/GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (CRESTT/GSFC/UMBC), G. Sato (GSFC/ISAS), G. Skinner (CRESST/GSFC/UMBC), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT
on 1 Feb 2008; 22:05 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

Subjects: X-ray, Binary, Transient, Pulsar

Referred to by ATel #: 1385, 1400, 1401

The Swift/BAT hard X-ray transient monitor reports an outburst of the X-ray pulsar GRO J1750-27 (also known as AX J1749.1-2639). The source was first detected at 0.031 +/- 0.005 cts/cm^2/sec (140 mcrab) in a 320-sec observation in the 15-50 keV energy range, beginning at 11:26:40 UT on Jan. 29, 2008 (MJD 54494). It has been observed above 100 mcrab in all pointings since this initial detection. The detection significances in individual pointings average 6-7 sigma. This source is normally below the BAT transient monitor detection threshold of 0.003 cts/sec/cm^2 (about 15 mcrab). GRO J1750-27 is currently too close to the sun to be observed with the Swift narrow-field instruments. The source was first detected in CGRO/BATSE in September 1995 (Scott et al, ApJ 488, 831, 1997) at a much lower level (< 30 mcrab). No outbursts have been reported since that time.

BAT Transient Monitor observations of GRO J1750-27