[vsnet-grb-info 7253] GRB 090118: Possible burst detection from Swift-BAT slew data

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8825
SUBJECT: GRB 090118: Possible burst detection from Swift-BAT slew data
DATE:    09/01/18 22:02:25 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 likely GRB candidate by the BAT Slew  
Survey (BATSS), pending confirmation by Swift XRT, in the slew that  
started at 13:54:02 UT and lasted 94 sec. The ground-calculated  
position is RA, Dec = 49.865, +18.478 deg, which is
RA (J2000) =  03h 19m 28s
Dec(J2000) = +18d 28' 40"
with an uncertainty of 3.69 arcmin (90% confidence, including  
systematics). The detection was triggered by simultaneous detections  
of 6.9 sigma and 8.0 sigma from imaging in the overlapping energy  
bands of 15-50 keV and 15-150 keV, respectively. The burst mask-tagged  
lightcurve in the 15-150keV band shows a broad emission peak starting  
at T+66 sec, lasting 19 sec, and peaking 3 times at T+71, T+74 and t+ T 
+81 sec. T90 = 16sec and T50 = 8sec.

The time-averaged spectrum over the exposure time of the source is  
best fit by a simple power law with photon index 1.35, and the fluence  
in the 15-150 keV band is 4.0 x 10^-7 erg/cm^2.

A follow-up Swift ToO observation has been scheduled to begin at 20:52  
UT, 6.97 hours after the burst. Optical/IR observers are encouraged to  
image this field as soon as possible as it is an early-evening object.