TITLE:   GCN CIRCULAR
NUMBER:  21805
SUBJECT: GRB 170903A: UAFO /ISON optical upper limit
DATE:    17/09/04 11:01:47 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed the field of  Swift GRB 170903A  (Markwardt et al., GCN 
21793) with SANTEL-650 (0.65m)  telescope  of UAFO/ISON-Ussuriysk 
observatory. We obtained several unfiltered images starting on  Sep. 03 
(UT) 13:20:15.  Within enhanced XRT position (Goad et al., GCN 21797) we 
do not detect any source.  Preliminary photometry of a combined image is 
following

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

2017-09-03 13:20:15  0.04847  CR      120*30    n/d  n/d   20.4


Photometry is based on nearby SDSS DR9 stars
SDSS_DR9_id         R(Lupton)
J165744.06+345751.4 16.01
J165803.01+345725.1 16.56
J165808.53+350159.7 15.58
J165749.08+345655.1 16.66
J165805.88+345230.1 16.24