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GCN Circular 3682

GRB050726: Swift-BAT detection of a weak burst
2005-07-26T13:08:21Z (19 years ago)
Scott Barthelmy at NASA/GSFC <>
S. Barthelmy (GSFC), D. Palmer (LANL), T. Sakamoto (GSFC), S.T. Holland (GSFC),
D. Burrows (PSU), M. Chester (PSU), S. Hunsberger (PSU), A. Moretti (OAB),
S. Covino (OAB), P. Romano (OAB), A. Antonelli (INAF-OAR), T. Poole (MSSL),
N. Gehrels (GSFC)
on behalf of the Swift team:

At 05:00:17 UT, Swift-BAT triggered and located GRB050726 (trigger=147788).
The spacecraft slewed immediately.  But since there was a gap in the TDRSS
coverage at the moment of the burst, the TDRSS messages were lost, and
therefore there were no real-time GCN notifications.  The following comes
from the analysis of the full data set after the regularly scheduled
data downlink pass.  The BAT ground-calculated location is RA,Dec
200.052,-32.072 {13h 20m 12s,-32d 04' 19"} (J2000), with an uncertainty
of 3 arcmin (radius, 90% containment, stat+sys).  The BAT light curve
shows a broad weak peak with a hint of structure with a total duration
of ~30 sec (starting before the trigger at ~T-15 extending to ~T+15 sec).
The power law photon index of the time-averaged spectrum is 1.04 +- 0.16.
The fluence in the 15-350 keV band are (4.3 +- 0.7) x 10^-6 erg/cm2.   
The 1-s peak photon flux measured from T0+1.0 second in the 15-350 keV  
band is (2.0 +- 0.4) ph/cm2/s.  All the quoted errors are at the 90%  
confidence level. 

An uncatalogued, fading X-ray source was detected by XRT at the following
position: RA,Dec 13h 20m 12.30s -32d 03m 50.8s} (J2000) with an uncertainty
of 6 arcsec (90% containment).  This is 28.4 arcsec from the BAT position
reported above.

The Swift Ultra-Violet/Optical Telescope (UVOT) observations began
at 05:02:07 UT, 110 seconds after the BAT trigger.  The first data
taken in the V band after the spacecraft settled was a 100 sec exposure 
with the midpoint of the observation at 223 sec after the BAT trigger. 
A comparison against the DSS catalogue reveals a possible new source
inside the BAT and XRT error circles 13h 20m 11.9s,-32d 03' 51.9" (J2000),
although this could also be a known source with a high proper motion.
The V band magnitude was 17.6 +- 0.2.

[GCN OPS NOTE(31jul05):  Per author's request, the Dec in the 3rd pragraph
was changed from "-3d" to "-32d".]
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