TITLE:   GCN CIRCULAR
NUMBER:  18398
SUBJECT: GRB 151006A: Swift detection of a burst
DATE:    15/10/06 10:05:37 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

D. Kocevski (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC),
P. A. Evans (U Leicester), K. L. Page (U Leicester) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 09:55:01 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 151006A (trigger=657750).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 147.451, +70.509, which is 
   RA(J2000)  =  09h 49m 48s
   Dec(J2000) = +70d 30' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single FRED-like peak
structure with a duration of about 40 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 09:55:50.4 UT, 48.6 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 147.4256, 70.5036 which is equivalent to:
   RA(J2000)  = +09h 49m 42.14s
   Dec(J2000) = +70d 30' 13.0"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 36 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. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 58 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
0.24. 

Burst Advocate for this burst is D. Kocevski (dankocevski AT gmail.com). 
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.)