TITLE:   GCN CIRCULAR
NUMBER:  23206
SUBJECT: GRB 180904A: AbAO optical upper limit
DATE:    18/09/05 16:18:22 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

A. Volnova  (IKI),  A. Pozanenko (IKI), R. Inasaridze (AbAO),  E. 
Mazaeva (IKI),  V. Ayvazian  (AbAO),  O. Kvaratskhelia (AbAO), G. 
Kapanadze (AbAO),  I. Molotov (KIAM) report on behalf of larger GRB 
follow-up collaboration:

We observed the field of the Swift GRB 180904A (D'Ai et al., GCN 23194) 
with AS-32 (0.7m) telescope of Abastumani Observatory starting on 
September 04 (UT) 21:52:23.   We do not detect any object within 
enhanced XRT position (Osborne et al., GCN 23196). Preliminary 
photometry of the field is following:

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

2018-09-04  21:52:23   0.05731   CR     70*60  n/d   n/d  21.5

The photometry is based on nearby USNO-B1.0 stars (R2 magnitude)
USNO-B.1_id    R2
1366-0296056   14.72
1366-0296068   15.43
1365-0287325   15.62
1366-0296106   15.21
1366-0296088   14.95
1366-0296093   14.37