TITLE:   GCN CIRCULAR
NUMBER:  14428
SUBJECT: GRB 130420A: ISON-NM optical observations
DATE:    13/04/21 03:58:45 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

L. Elenin (KIAM),  A. Volnova ( IKI),  V. Savanevych (KNURE),   A. 
Bryukhovetskiy (NSFCTC),  I. Molotov (KIAM), A. Pozanenko (IKI) report on 
behalf of  larger GRB  follow-up collaboration:

We observed the field of  the Swift GRB 130420A (Page et al., GCN 14406) 
with 0.45-m telescope of ISON-NM observatory  on Apr. 20,  between (UT) 
07:30:54 - 10:51:49.  The observation started automatically 144 s after 
burst trigger. We took  several unfiltered images of  30, 60 and 300 s 
exposures.  The optical counterpart of GRB 130418A (Guidorzi et al., GCN 
14405; Page et al., GCN 14406; Guver et al., GCN 14407) is clearly visible 
in single images.

Coordinates of the counterpart are (J2000) RA = 13:04:25.56 Dec = 
+59:25:26.8 with uncertainties of 0.2" coincide with the coordinates 
reported early  (Guidorzi et al., GCN 14405, Guver et al., GCN 14407).

A photometry of single and later combined  image is based  on the SDSS stars 
with assumed R-magnitude
J130421.49+592547.6 R = 16.13
J130416.49+592509.2 R = 16.95
J130443.88+592659.3 R = 14.54

Preliminary light curve can be found at 
http://grb.rssi.ru/GRB130420A/GRB130420A_lightcurve_ISON-NM.png
The light curve is clearly exhibit a fast rise and peaked with 16.1 mag at 
~0.0207days after burst trigger following steep power law decay and later at 
0.05 days swallowing to the typical afterglow power law.