TITLE: GCN CIRCULAR NUMBER: 8600 SUBJECT: GRB 081203A: Burst detection from Swift-BAT slew data DATE: 08/12/03 18:54:02 GMT FROM: Antonio Copete at Harvard U A. Copete, J. Grindlay (Harvard) S. Barthelmy, C. Markwardt, N. Gehrels (NASA/GSFC) We report the detection of a GRB candidate by the BAT Slew Survey (BATSS) in the slew that started at 13:52:02 UT. This is 309 sec before the trigger time for the GRB that followed (A. M. Parsons et al, GCN 8595), which occurs at a different location and should hereafter be referred to as GRB 081203B. The ground-calculated position of GRB 081203A is RA, Dec = 228.789, +44.427 deg, which is RA (J2000) = 15h 15m 09s Dec (J2000) = +44d 25' 36" with an uncertainty of 3.04 arcmin (90% confidence, including systematics). The detection was triggered by simultaneous independent detections of 11.0 sigma and 5.6 sigma from imaging in the 15-50 keV and 50-150 keV energy bands, respectively. The burst mask- tagged lightcurve shows 2 main peaks, the larger one at T+24sec and lasting 2sec as the burst enters the BAT FoV, the second one at T +30sec with a duration of 2sec, and it has largely faded as the pointing observation that follows begins. The measured T90 = 23.4sec and T50 = 8.2sec (15-150keV). Preliminary spectral analysis from T+24.0 to T+50.4 shows a time- averaged spectrum that is best fit by a simple power law with photon index of 1.65. The total fluence in the 15-150 keV band is 2.1 x 10^-6 erg/cm2, and the 1-sec peak flux is 3.5 x 10^-7 erg/cm2/sec. A follow-up Swift ToO observation has been scheduled to begin at 18:26 UT, 4.6 hours after the burst.