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Swift/BAT detects increased activity from accreting pulsar H 1553-542

ATEL # 1345; H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (CRESST/GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. Markwardt (CRESST/GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), K. Pottschmidt (CRESST/GSFC/UMBC), T. Sakamoto (CRESTT/GSFC/UMBC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team
on 31 Dec 2007; 23:27 UT
Password Certification: Hans A. Krimm (

Subjects: X-ray, Binaries, Pulsars, Transients

The Burst Alert Telescope on Swift has detected increased activity from a position associated with the accreting pulsar H 1553-542 (Apparao, K. M. V., et al, Nature, 271, 225, 1978). The source first became detectable to Swift-BAT in daily averages on 8 December 2007 and had a bright outburst to 0.039 +/ 0.007 cts/sec/cm^2 (170 mcrab) on 12 December. Since 21 December, the source has been detectable above 50 mcrab (0.011 cts/sec/cm^2) with large fluctuations. Prior to the current outburst the source had been undetectable in BAT to a level of 0.003 cts/sec/cm^2 (about 15 mcrab). The best BAT position is RA=239.40, dec=-54.40 (J2000), 2.1 arc minutes from the position of H 1553-542 listed in Simbad (RA=239.4550, dec= -54.4144). Since this is within the uncertainty in BAT locations in the transient monitor, we associate the BAT monitor source with H 1553-54. Using SAS 3 observations, Kelley, R.L., Rappaport S., and Ayasli S., (Ap. J., 274, 765, 1983) reported 9.3 second pulsations from H 1553-542 and tentatively identified it as a Be/X-ray binary system. There have been no outbursts reported in the literature since 1975.

Swift BAT transient monitor observations of H 1553-542

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R. E. Rutledge , Editor
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