TITLE:   GCN CIRCULAR
NUMBER:  19605
SUBJECT: GRB 160625B: TSHAO optical observations
DATE:    16/06/27 19:59:50 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

E. Mazaeva (IKI), A. Kusakin (Fesenkov Astrophysical Institute), P. 
Minaev (IKI), I. Reva (Fesenkov Astrophysical Institute), A. Volnova 
(IKI), A. Pozanenko (IKI) report on behalf of larger GRB follow-up 
collaboration:

We observed the field of GRB 160625B (Dirirsa et al., GCN 19580; Burns 
et al. GCN 19581) with Zeiss-1000 (East) 1-m telescopes of Tien Shan 
Astronomical Observatory. We obtained several images in R filter 
starting on June 26 (UT) 19:39:18. We detect optical afterglow of  GRB 
160625B (Troja et al., GCN 19588; Oates  et al., GCN  19589). 
Preliminary photometry of a combined image is following

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

2016-06-26 19:39:18   0.91784 R       50*120 19.07  0.05  22.0

Photometry is based on nearby USNO-B1.0 stars
USNO-B.1_id  R2
0969-0608423 16.38
0969-0608416 16.28
0969-0608335 15.00
0969-0608366 16.05
0969-0608449 17.38
0969-0608443 16.78
0969-0608456 16.79

The GRB 160625B triggered Fermi LAT and GBM (Dirirsa et al., GCN 19580; 
Burns et al. GCN 19581), Konus-Wind (Svinkin et al. GCN 19604) and  D. 
Kann (GCN 19579) reported about CALET and SPI-ACS/INTEGRAL trigger.

A light curve of SPI-ACS/INTEGRAL  can be found in
http://grb.rssi.ru/GRB160625B/GRB160625B_API-ACS.png

The SPI-ACS time profile of  GRB 160625B consists of 3 episodes of total 
duration about 750 seconds and compatible with time profiles reported by 
GBM (Burns, GCN 19581) and Konus-Wind (Svinkin et al. GCN 19604).