[AAVSO-HEN] GRB 090306B: Burst detection from Swift-BAT slew data

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TITLE:   GCN CIRCULAR
NUMBER:  8944
SUBJECT: GRB 090306B: Burst detection from Swift-BAT slew data
DATE:    09/03/07 16:50:40 GMT
FROM:    Antonio Copete at Harvard U  <acopete at head.cfa.harvard.edu>

A. Copete, J. Grindlay (Harvard)
S. Barthelmy, C. Markwardt, N. Gehrels (NASA/GSFC)

We report the detection of a bright GRB by the BAT Slew Survey (BATSS)  
in the slew that started at 23:07:02 and lasted 66 sec. The ground- 
calculated position is RA, Dec = 231.204, -6.958 deg, which is
RA (J2000) = 15h 24m 49s
Dec(J2000) = -06d 57' 29"
with an uncertainty of 2.87 arcmin (90% confidence, including  
systematics). The detection was triggered by simultaneous independent  
detections of 35.6 sigma and 20.2 sigma from imaging in the 15-50 keV  
and 50-150 keV energy bands, respectively. The burst mask-tagged  
lightcurve lightcurve in the 15-150 keV band shows a strong and broad  
emission peak starting at T+21sec, lasting 29 sec, and peaking twice  
at T+25sec and T+30sec. T90 = 20.4sec and T50 = 8.0sec.

The time-averaged spectrum over the 55 sec exposure time of the source  
is best fit by a power law with an exponential cutoff, with photon  
index 1.02 and high-energy cut at 133 keV. The fluence in the 15-150  
keV band is 3.1 x 10^-6 erg/cm^2, and and the peak 1-sec flux is 2.5   
10^-7 erg/cm^2/sec at T+30sec. A follow-up Swift ToO observation for  
this burst has been scheduled.