TITLE:   GCN CIRCULAR
NUMBER:  14645
SUBJECT: GRB 130427A: optical observations
DATE:    13/05/14 20:23:42 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

A. Volnova (IKI), I. Korobtsev (ISTP), E. Klunko (ISTP), A. Pozanenko 
(IKI)  on behalf of  larger GRB  follow-up collaboration:

We continue observation of the Swift GRB 130427A (Maselli et  al., GCN 
14448)  with AZT-33IK telescope of Sayan observatory (Mondy). The 
afterglow (Elenin et al. GCN 14450, Perley GCN 14451) is clearly 
detected. The brightness of the afterglow+host  is following:

UT start,            t-t0       Filter Exp.   OT
                     (mid, days)        (s)    (mag.)

2013-05-13T15:20:00  16.3346   R      3600    20.66 +/- 0.06
2013-05-14T14:24:35  17.2968   R      3600    20.63 +/- 0.07

The photometry is based on the same star  reported by Rumyantsev et al. 
(GCN 14582). After subtraction  of a suggested brightness (R, Vega)of 
the host galaxy (e.g. Watson et al., GCN 14606; Kann et al., GCN 14631) 
from our photometric values, our light curve can be approximated (in 
general)  by a single power law   starting at ~ 0.6 days after burst 
trigger.  Indeed our early observations suggest some flattening between 
6.5 - 13 days (Xu et al., GCN 14597; Kann et al., GCN 14631). It could 
be due to a SN or due to a wide bump analogous to bumps observed early 
in the light curve.  However photometry is still preliminary and more 
detailed calibration/intercalibration is necessary.