[vsnet-grb-info 2071] GRB050904: Swift-BAT detection of a probable burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3910
SUBJECT: GRB050904: Swift-BAT detection of a probable burst
DATE:    05/09/04 03:07:21 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

J. Cummings (GSFC/NRC), L. Angelini (GSFC), S. Barthelmy (GSFC), A. Cucchiara (PSU),
N. Gehrels (GSFC), C. Gronwall (PSU), S.T. Holland (GSFC), V. Mangano (INAF-IASF),
F. Marshall (GSFC), C. Pagani (PSU), D. Palmer (LANL)
on behalf of the Swift team:

At 01:51:44 UT, Swift-BAT triggered and located GRB050904 (trigger=153514).
The spacecraft slewed immediately.  The BAT on-board calculated location
is RA,Dec 13.670d,+14.138d {00h 54m 41s,+14d 08' 17"} (J2000), with an
uncertainty of 3 arcmin (radius, 90% containment, stat+sys).  This was a 64-sec
image trigger.  The BAT light curve shows hints of emission, but it is
not possible to separate source variations from background variations
at this early stage in the analysis.  Given that this is at high galactic
latitude, we believe this is a burst rather than a hard x-ray transient.
There is nothing in SIMBAD nor in the BAT Active Source list near this location.

XRT slewed promptly to the target and observation started at 01:54:25 UT
(T+161 sec) with XRT in auto state.  XRT revealed an uncatalogued fading
point source at RA (J2000): 00h 54m 50.4s  Dec (J2000): +14d 05' 08.5"
with an uncertainty of 6 arsec (radius), 3.9 arcmin from the BAT position.

The UVOT began observing at 01:54:28 UT, 164 s after the BAT trigger.
The UVOT image is 3 arcmin away from the XRT position, so it does not
intersect the XRT or BAT error circle.  We cannot tell whether there
is an optical counterpart at this time.

We are currently in the portion of the orbits where the spacecraft does not 
pass over the Malindi downlink station.  Therefore, it will be 4 hours
before we have access to the full data set for the refined analyses.