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THE ASTRONOMER Electronic Circular No 3105      2015 Sep 10 12.54UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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GRB 150910A WITH OPTICAL COUNTERPART
C. Pagani et. al., relay on GCN 18264 on behalf of the Swift team
that at 2015 Sept 10, 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 as:
RA(J2000) = 00h 22m 42s Dec(J2000) = +33d 29' 55"
with an uncertainty of 3 arcmin.

The XRT began observing the field at 09:07:14.1 UT, 145.3 seconds after the
BAT trigger and found a bright, uncatalogued X-ray source located at:
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
DEC(J2000) = +33:28:21.9 with a 90%-confidence error radius of about 0.71
arc sec. 

The KAIT GRB team relay on GCN 18265:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick
Observatory, responded to Swift GRB 150910A starting at 09:34:20 UT, ~30
minutes after the burst. Observations were performed with an automatic
sequence in the clear (roughly R), V, and I filters, and the exposure time
was 20-s per image. The UVOT afterglow reported by Pagani et al. was clearly
detected in all filters. The brightness is about R~16.2 mag at ~30 minutes
after the burst, and is decreasing.

Editor: The rate of optical decline is unclear but the field is worth an
image as soon as it is dark. Please relay the image and any measurements to
the Editor


Guy M Hurst