GCN Circular 10130

P.A. Curran (MSSL-UCL), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), S. Campana (INAF-OAB),
P. A. Evans (U Leicester), C. Guidorzi (U Ferrara),
J. A. Kennea (PSU), V. Mangano (INAF-IASFPA), J. Mao (INAF-OAB),
P. T. O'Brien (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. Rowlinson (U Leicester) and M. H. Siegel (PSU)
report on behalf of the Swift Team:

At 08:49:22 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 091104 (trigger=374875).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 208.742, +47.398 which is 
   RA(J2000) = 13h 54m 58s
   Dec(J2000) = +47d 23' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, there
is no obvious variation in the immediately available light curve. 

The XRT began observing the field at 08:51:34.2 UT, 131.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 208.75600, 47.41126 which
is equivalent to:
   RA(J2000)  = 13h 55m 1.44s
   Dec(J2000) = +47d 24' 40.5"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 58 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.72e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.85e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with
the White filter starting 139 seconds after the BAT trigger. No
credible afterglow candidate has been found in the initial data
products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. 
The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8'
region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about
18 mag. No correction has been made for the expected extinction
corresponding to E(B-V) of 0.01. 

Burst Advocate for this burst is P.A. Curran (pac AT mssl.ucl.ac.uk). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)