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Announcement of the Swift/BAT Hard X-ray Transient Monitor

ATEL # 904; H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. D. Barthelmy (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), D. Sanwal (GSFC/JHU), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team
on 1 Oct 2006; 20:57 UT
Password Certification: Hans A. Krimm (

Subjects: X-ray, AGN, Binaries, Cataclysmic Variables, Pulsars, Quasars, Transients

The Burst Alert Telescope (BAT) on the Swift satellite is a large field of view instrument that continually monitors the sky to provide the gamma-ray burst trigger for Swift. An average of more than 70% of the sky is observed on a daily basis. These survey mode data in the 15-50 keV energy band are analyzed to derive count rates for 221 known hard X-ray sources on time scales ranging from one minute to 24 hours. Light curves for each source are produced on two timescales: a single Swift pointing (approximately 20 minutes) and the weighted average for each day. The light curves are available in graphical, FITS and ascii formats. The data are processed after each satellite data downlink (every ~90 minutes, except during the daily data gaps of ~6 hours duration) and the on-line light curves are updated after each round of processing.

The minimum detectable flux in the transient monitor depends on both the duration of the exposure and the position of the source in the sky. For the median Swift pointing duration of 736 sec and a source near the center of the BAT field of view, a 3-sigma detection corresponds to a flux of 0.006 cts/cm^2/sec, or approximately 27 mCrab. In the daily averages, a 3-sigma detection for a source near the center of the BAT field of view corresponds to 0.0013 cts/cm^2/sec, or approximately 6 mCrab.

The light curves are available through the Swift mission web page at Full information about the processing, data corrections and systematic errors can be found by clicking the "README" link at the top of the page.

The Swift/BAT Hard X-ray Transient Monitor

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