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GX 354-0 is rising in hard X rays

ATEL # 1030; H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team
on 14 Mar 2007; 22:05 UT
Password Certification: Hans A. Krimm (

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

Swift-BAT reports that the LMXRB GX 354-0 (also known as 4U 1728-34) is rising in flux in the 15-50 keV X-ray band. This source is highly variable in the BAT on time scales of weeks, typically varying between 20 and 80 mCrab with an average value of 50 mCrab and some excursions above 100 mCrab. However on about March 3, 2007 (MJD 54162) the flux began rising steadily and it is now above 200 mCrab in the daily average, which is the highest value that BAT has seen since it began its transient monitor program in February 2005.

We also see a large number of BAT rate triggers from GX 354-0 (10 bursts from March 9-12, 2007), which we identify as probable thermonuclear X-ray bursts. The bursts show a fluence of ~1 Crab on time scales of 1-4 seconds, most strongly in the 15-25 keV energy band. We note similar bursting episodes in September 17-25, 2006 and October 29 to November 3, 2006, although the daily average flux during these episodes peaked at 170 mCrab with a mean of 120 mCrab.

The bursting activity and the increase of the persistent level is distinct from the Rapid Burster (MXB 1730-33), which is within 32 arcminutes of GX 354-0, but spatially resolved by BAT.

The last time such a high flux was reported for GX 354-0 was on February 24, 2004 when IBIS on INTEGRAL reported a similar behavior and peak flux (ATEL #248). At that time the flux subsequently decayed by a factor of five within the next week suggesting that this flaring behavior may be short-lived.

BAT Hard X-ray Transient Monitor for GX 354-0

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R. E. Rutledge , Editor
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