TITLE:   GCN CIRCULAR
NUMBER:  17341
SUBJECT: GRB 150120A: ISON-NM early optical limit
DATE:    15/01/21 18:22:16 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

L. Elenin (KIAM),  E. Mazaeva (IKI), A. Volnova (IKI), I. Molotov 
(KIAM), A. Pozanenko (IKI) report on behalf of larger GRB  follow-up 
collaboration:

We observed the field of the Swift GRB 150120A (D'Elia et al.,
GCN 17310) with 0.4-m telescope of ISON-NM observatory in robotic mode 
starting on Jan., 20 (UT) 02:58:58, i.e. 72 seconds after burst trigger. 
We obtained 60 unfiltered images of 30 s exposure. We do not detect any 
source within enhanced XRT error circle (Evans et al., GCN 17317):

Date      UT start   t-T0         Exp.    Filter  UL (3sigma)
                      (mid.,days)    (s)
2015-01-20 02:58:58  0.00227      5*30    Clear   19.0
2015-01-20 02:58:58  0.01950     60*30    Clear   20.2


The photometry is based on nearby SDSS DR9 stars

SDSS9_id                R_Lupton
J004136.43+340051.9     15.61
J004135.94+335950.0     14.56
J004101.23+335851.1     15.84