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Swift/BAT Reports Increased Activity from 4U 1724-307

ATEL # 1395; 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),
on 22 Feb 2008; 20:55 UT
Password Certification: Hans A. Krimm (

Subjects: X-ray, Binaries, Neutron Stars, Transients

The Swift/BAT hard X-ray transient monitor reports an outburst of the X-ray burster 4U 1724-307 (also known as GRS 1724-308) in the globular cluster Terzan 2. Since Feb. 16, 2008 (MJD 54512), the source has been seen at an average rate of 0.015 +- 0.001 cts/cm2/sec (65 mcrab) in the 15-50 keV energy band, with some peaks as high as 150 mcrab. The source is normally detected in the BAT at ~17 mcrab.

We note that the RXTE All-Sky Monitor web site shows that rate for 4U 1724-307 approximately doubled in mid-December 2007 from 2 cts/sec to 4 cts/sec and is now declining.

The last previous report of an outburst from this source was in February 2004 (ATel #237, #241).

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