Swift/BAT detects a new outburst of the transient accreting pulsar GS 1843-02

ATel #4350; H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), W. Baumgartner (CRESST/GSFC/UMBC), J. Cummings (CRESST/GSFC/UMBC), N. Gehrels (GSFC), C. B. Markwardt (GSFC), D. Palmer (LANL), T. Sakamoto (Aoyama Gakuin Univ.), M. Stamatikos (OSU/GSFC), J. Tueller (GSFC), T. Ukwatta (MSU)
on 31 Aug 2012; 20:35 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

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The Swift/BAT hard X-ray transient monitor has recorded a recent flux increase from the transient X-ray pulsar and Be binary system GS 1843-02 (also known in the literature as X 1845-024, 2S 1845-024 and GRO J1849-03). In the 15-50 keV band, the source was first detected on 2012 August 22 (MJD 56161). It reached a peak of 0.009 +/- 0.002 ct/s/cm^2 (~40 mCrab) on August 27 and has since started to decline, reaching 0.003 +/- 0.002 ct/s/cm^2 (~15 mCrab) on August 31. This source was not in the BAT monitor catalog and had not reached the threshold for detection as an "unknown" source before this. That threshold is approximately 0.010 ct/s/cm^2 for 1-day and 0.006 ct/s/cm^2 for a 2-day average.

The source had regular outbursts in the 1990's, as reported by Finger et al, ApJ, 517, 449 (1999). Examination of the Swift/BAT monitor archives from Jan. 2010 onward reveals weaker outbursts (peak ~20 mCrab) in Feb. 2010, Jan. 2011 and Dec. 2011. The spacing between these outbursts is longer than the orbital period of 242.18 days reported by Finger (1999). Only the first of the BAT outbursts matched an outburst in the RXTE/ASM. The ASM recorded an outburst in August 2011 which was not seen in BAT. The source has never been detected in on-board processing.

We are planning to complete the analysis of the archival BAT monitor data and then search for a periodicity in the BAT data.

Swift/BAT Hard X-ray Transient light curve for GS 1843-02