GCN Circular 8600

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
Not found
 
 
), 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.