TITLE:   GCN CIRCULAR
NUMBER:  26965
SUBJECT: GRB 200131A: ISON-Castelgrande optical observations
DATE:    20/02/02 21:30:37 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

A. Pozanenko (IKI), S. Schmalz (KIAM),  V. Kim (AFIF, Pulkovo 
Observatory),  E. Mazaeva  (IKI), A. Volnova (IKI),  I. Molotov (KIAM) 
report on behalf of larger GRB follow-up collaboration:

We observed the field of the  GRB 200131A   (Sbarufatti al., GCN  26953) 
  with  ORI-22 telescope of ISON-Castelgrande observatory starting on 
Jan. 31  (UT) 23:11:28.  We obtained 120 images of 60 s exposure in 
Clear filter.  The optical afterglow  (Sbarufatti al., GCN  26953; 
Lipunov  al., GCN  26954; Butler al., GCN  26957; Strausbaugh al., GCN 
26959; Kuin al., GCN  26962)   is best detected in the stacked image of 
the first 60 images.
Preliminary photometry  of the  afterglow  is following

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

2019-01-31 23:11:28   0.04353     Clear 60*60  18.35 0.25

The photometry is based on nearby USNO-B1.0  stars  (R2 magnitude).