GCN Circular 21966

S. B. Cenko (GSFC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), A. A. Breeveld (UCL-MSSL),
P. A. Evans (U Leicester), J.D. Gropp (PSU), K. L. Page (U Leicester)
and M. H. Siegel (PSU) report on behalf of the Swift Team:

At 07:55:32 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 171004A (trigger=776347).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 139.162, +52.680, which is 
   RA(J2000)  =  09h 16m 39s
   Dec(J2000) = +52d 40' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for image triggers, there is nothing
significant in the real-time light curve. 

The XRT began observing the field at 07:58:26.9 UT, 174.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 139.1713, 52.6937 which is equivalent to:
   RA(J2000)  = +09h 16m 41.11s
   Dec(J2000) = +52d 41' 37.3"
with an uncertainty of 4.9 arcseconds (radius, 90% containment). This
location is 53 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 3.22e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of  52 seconds with the White filter
starting 184 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
0.02. 

Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov). 
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.)