[vsnet-grb-info 16983] GRB 150910A: Swift detection of a burst with an optical afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18264
SUBJECT: GRB 150910A: Swift detection of a burst with an optical afterglow
DATE:    15/09/10 09:26:53 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

C. Pagani (U Leicester), A. P. Beardmore (U Leicester),
A. A. Breeveld (UCL-MSSL), K. L. Page (U Leicester),
P. Romano (INAF-IASFPA) and T. N. Ukwatta (LANL) report on behalf of
the Swift Team:

At 09:04:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150910A (trigger=655097). Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 5.675, +33.499 which is 
   RA(J2000) = 00h 22m 42s
   Dec(J2000) = +33d 29' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). As is typical for image triggers, the real-time
light curve does not show anything significant. 

The XRT began observing the field at 09:07:14.1 UT, 145.3 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 5.6669, 33.4717 which is equivalent to:
   RA(J2000)  = +00h 22m 40.06s
   Dec(J2000) = +33d 28' 18.1"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). This
location is 101 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 153 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	00:22:40.14 =	5.66723
  DEC(J2000) = +33:28:21.9  =  33.47275
with a 90%-confidence error radius of about 0.71 arc sec. This position is 3.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
20.27 with a 1-sigma error of about  0.18. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.05. 

Burst Advocate for this burst is C. Pagani (cp232 AT star.le.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.)