TITLE:   GCN CIRCULAR
NUMBER:  20886
SUBJECT: GRB 170317A: ISON-Ussuriysk aferglow confirmation
DATE:    17/03/17 13:06:50 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

E. Mazaeva (IKI), A. Pozanenko (IKI), A. Kochergin (UAFO), A. Volnova 
(IKI),  E. Chornaya  (UAFO),   A. Matkin (UAFO, ISON),  I. Molotov 
(KIAM)  report on behalf of larger GRB follow-up collaboration:

We observed the field of the GRB 170317A (LaPorte et al., GCN  20885) 
with SANTEL-650 (0.65m)  telescope of UAFO/ISON-Ussuriysk observatory 
starting on March, 17 (UT) 10:20:37. We obtained series of unfiltered 
images of 60 s exposure. In a first combined images we  detected optical 
afterglow (LaPorte et al., GCN  20885). Preliminary photometry of some 
initial combined image  is following

Date       UT start  t-T0   Filter  Exp.  OT     err  UL (3sigma)
                      (mid, days)    (s)

2017-03-17 10:20:37  0.0321 none   20*60  18.95  0.08 21.5

In comparison with early reported photometry (LaPorte et al., GCN 
20885) the OT is faded, and we confirm the afterglow of the GRB 170317A.

Photometry is based on nearby USNO-B1.0 stars

USNO_B1_id   R2
1405-0167482 15.08
1405-0167474 15.43
1405-0167493 16.10
1405-0167484 16.14
1404-0169177 15.93
1405-0167639 15.62
1405-0167631 15.69