[vsnet-grb-info 14080] Swift 575905/GRB 131026A: optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15394
SUBJECT: Swift 575905/GRB 131026A: optical observations
DATE:    13/10/28 17:52:28 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

A. Volnova (IKI), R. Inasaridze (AAO), G. Inasaridze (AAO), V.
Zhuzhunadze (AAO), Yu. Krugly (IA KhNU), I. Molotov (KIAM), A. Pozanenko 
(IKI) report on behalf of larger GRB follow-up collaboration:

We observed the field of Swift Trigger 575905/GRB 131026A (Cenko et al., 
GCN 15384)  with AS-32 telescope of Abastumani Observatory starting 
Oct., 26 (UT) 21:06:35. We obtained several unfiltered images with 
exposures of 180 s. We investigated stacked image and found that both 
XRT sources (Izzo et al., GCN 15388) coincide with known optical 
sources, i.e.

source 1 (XRT) = SDSS J010222.74+323005.0 (01:02:22.75 +32:30:05.0)
source 2 (XRT) = TYC 2281-1221-1 (01 02 02.468 +32 30 01.53)

Within BAT error circle (Cenko et al., GCN 15384) we found a point-like 
source which is not presented in SDSS catalog. Coordinates of the source 
are (J2000) RA=   01 02 14.64, Dec = +32 30 35.7  with uncertainties of 
0.2 arcsec in both coordinates. The details of the photometry of the 
source  are the following:

UT start    t-T0       Filter Exp.     OT              UL (3 sigma)
            (mid, days)         (s)

21:06:35   0.64270     None   32x180   21.67 +/- 0.08  22.6

The photometry is based SDSS stars, R (gri -> R transformations by
Lupton 2005):

SDSS id                   R(Lupton)
J010212.32+323137.9       18.988
J010208.62+323107.7       17.448
J010155.76+322851.8       17.317

We subdivide total number of images in two combined images and compare 
astrometry and photometry of the two combined images. One can conclude 
that the upper limit of a proper motion of the source is 3 arcsec per 50 
minutes, and one can marginally suggest that brightness of the source is 
increased at ~0.3m between the two combined images.

Finding chart can be found in 
http://grb.rssi.ru/GRB131026A_Swift_575905/GRB131026A_chart2.png

Additional observations in optic and X-ray are encouraged.