TITLE:   GCN CIRCULAR
NUMBER:  9539
SUBJECT: GRB 090618: ZTSh optical observations
DATE:    09/06/21 01:01:06 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

V. Rumyantsev (CrAO), A. Pozanenko (IKI)  report on behalf of larger GRB 
follow-up collaboration:

We observed the afterglow (Schady  et al., GCN 9512; Cenko et al., GCN 9513; 
Perley, GCN 9514; Rujopakarn et al., GCN 9515) of  the Swift GRB 090618 
between  (UT) Jun. 18  19:51 -  Jun. 19 00:51 with Shajn telescope of  CrAO. 
We detect afterglow in every  BVRI of 60 s exposure images of the series. 
Coordinates of the afterglow are RA(J2000):  19 35 58.77 Dec(J2000): +78 21 
24.2 with uncertainties of  0.3 arcsec.

Preliminary photometry of selected images based on USNO-B1.0 star 
1683-0077955  (RA=19 36 36.34   Dec=+78 21 07.00) assuming R=16.57  is 
following:

T0+     Filter, Exposure, mag.,     err.
(d)             (s)

0.4763   R       60     18.60 +/-0.05
0.5680   R       60     18.87 +/-0.03
0.6496   R       60     19.17 +/-0.04
0.6796   R       60     19.19 +/-0.10

The power low index of light curve approximation between 0.48 - 0.65 days 
is ~ -1.6, while after  0.65 days after burst onset we observe flattening of 
the light curve. A finding chart can be found at 
http://grb.rssi.ru/GRB090618/GRB090618_090618_R_ZTSh.gif