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GCN Circular 12333

Subject
GRB 110731A: SAO RAS and Terskol observations
Date
2011-09-09T08:30:16Z (13 years ago)
From
Vladimir Sokolov at SAO RAS <sokolov@sao.ru>
A. S. Moskvitin, V. V. Sokolov, O. I. Spiridonova (SAO RAS, Russia),
M. V. Andreev, A. V. Sergeev, N. A. Parakhin (Terskol Branch of Institute of
Astronomy, Russia)

We observed the field of GRB 110731A (Oates et al., GCN 12215) on July, 31
with 0.6-m Zeiss-600 (Terskol Branch of Institute of Astronomy,  Russia)
equipped with the PixelVision Vienna CCD (1024 x 1024, bin 2 x 2)
+ R filter, and 1-m Zeiss-1000 (SAO RAS, Russia) equipped with the
E2V 42-40 CCD (2048 x 2048, bin 2 x 2) + B and Rc filters. In both cases
the observations carried out at a high airmass and with the seeing ~4".

At all stacked images we did not detect any source within the Swift/UVOT
error circle (Oates., GCN 12222). Close to the error circle are visible two
objects which are also present in the USNO-B.1 catalogue:
S1: USNO-B.1 0614-0802286 (R.A.=18:42:00.72, Dec.=-28:32:14.9, E.=2000.0) &
S2: USNO-B.1 0614-0802328 (R.A.=18:42:01.24, Dec.=-28:32:11.6, E.=2000.0).
Our astrometric calibration and photometry of S1 object showed
that it can contain flux from OT but due to large seeing we can not
distinguish bright S1 and faint OT.

All three co-added images are shown at
ftp://ftp.sao.ru/pub/grb/GRB110731A/GRB110731A.jpg
Upper limits are shown at the following table.
_________________________________________________________
mid. time, UT   filter exp., sec  3-sigma lim. telescope
_________________________________________________________
19:15           R      53 x 200   19.9        Zeiss-600
19:24           Rc     31 x 60    21.7        Zeiss-1000
19:38           B      22 x 60    20.8        Zeiss-1000
_________________________________________________________

We use USNO-B.1 star 0614-0802353 (R.A.=18:42:01.83, Dec.-28:32:23.9,
E.=2000.0,  B2 = 15.77, R2 = 14.29) as a standard, and did not apply Galaxy
extinction correction.

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