[vsnet-grb-info 13871] GRB 130831A: ISON-UAFO optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15185
SUBJECT: GRB 130831A: ISON-UAFO optical observations
DATE:    13/09/07 23:20:51 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

A. Volnova (IKI), A. Matkin (UAFO, ISON), A. Stepura (UAFO, ISON), I. 
Molotov (KIAM), A. Pozanenko (IKI) report on behalf of  larger GRB 
follow-up collaboration:

We observed the afterglow (Hagen et al., GCN  15139; Guidorzi et al., 
GCN 15140) of the Swift GRB 130831A (Hagen et al., GCN  15139) with 
SANTEL-650 (0.65m) and VT-50 (0.5m)  telescopes of UAFO/ISON-Ussuriysk 
observatory  starting on  Aug. 31  (UT) 13:14:32, i.e. 10.3  minutes 
after burst trigger.  We took unfiltered  images of 120s and 30s 
exposures  ending observations at (UT) 19:20:53.

In each initial frames we clearly detect afterglow. A preliminary 
photometry of the afterglow in the initial frames are following

T_start              T0+       Filter, Exposure, OT,    OT_err
(UT)                 (mid, d)            (s)

2013-08-31T13:14:32  0.00782   none    120       13.86  0.02
2013-08-31T13:l6:40  0.00931   none    120       13.75  0.02
2013-08-31T13:18:49  0.01080   none    120       13.78  0.02

The photometry is based on reference stars SDSS-DR9, (R mag, 
transformation by Lupton 2005)

N	SDSS id			R(Lupton)errR
1	J235443.71+292539.3	13.491	 0.016
2	J235438.60+292547.3	14.136	 0.015
3	J235423.64+292452.8	17.120	 0.016