[vsnet-grb-info 2169] GRB050922B: Swift-BAT detection of a weak long burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4008
SUBJECT: GRB050922B: Swift-BAT detection of a weak long burst
DATE:    05/09/22 16:13:40 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

J. Norris (GSFC), L. Barbier (GSFC), S. Barthelmy (GSFC), P. Boyd (GSFC),
D. Burrows (PSU), J. Cummings (GSFC/NRC), N. Gehrels (GSFC),
S.T. Holland (GSFC/USRA), J. Kennea (PSU), H. Krimm (GSFC/USRA),
F. Marshall (GSFC), O. Godet (U. Leicester), D. Palmer (LANL),
T. Sakamoto (GSFC)
on behalf of the Swift team:

At 15:02:00 UT, Swift-BAT triggered and located GRB050922B (trigger=156434).
This was an image trigger with a 168-sec duration.  The spacecraft slewed
immediately after the end of the image trigger.  The BAT on-board
calculated location is RA,Dec 5.800d,-5.599d {00h 23m 12s,-05d 35' 55"} (J2000),
with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys).
The TDRSS lightcurve does not show any significant emission, but these
lightcurves are problematic for long image triggers.  We will have to wait
for the full Malindi data set (~8 hrs) to make a mask-tagged lightcurve.
We note that this source is at a high galactic latitude of -67 degrees.
We also note that the recent long-duration image trigger GRB 050904
was at high redshift.

XRT began observing the field at 15:07:42, 342 seconds after the BAT trigger.
Onboard centroiding found a bright fading uncatalogued X-ray source
in the field of view at the following coordinates:
RA(J2000):   0:23:13.3,
Dec(J2000): -5:36:12.9.
We estimate the uncertainty of this position to be 8 arcseconds (radius, 90% 
containment).  This position is 26 arcseconds from the BAT position above. 

UVOT began observing at 343 sec after the trigger.  The small UVOT TDRSS image
does not overlap the BAT error circle.   However, the full-field UVOT source
list contains only catalogued sources, in particular no source is found inside
the XRT error circle.  At the present time it is not possible to determine
a limiting magnitude for this field.  The V-band extinction in this direction
is A_V = 0.12 mag.