TITLE:   GCN CIRCULAR
NUMBER:  21203
SUBJECT: GRB 170604A: AbAO optical observations
DATE:    17/06/05 15:48:31 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed the field of the Swift  GRB 170604A (Page et al., GCN 21191) 
  with AS-32 (0.7m) telescope of Abastumani Observatory starting on 
June, 04 (UT)  23:52:07. We obtained several unfiltered images of the 
field.   Within enhanced XRT error circle  (Page et al., GCN   21196) we 
detected the afterglow (Izzo et al, GCN 21192; Izzo et al, GCN 21197; 
Schady, , GCN 21200). Preliminary photometry of the afterglow is following

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

2017-06-04 23:52:07   0.19950   CR     5*60  19.13 0.18  21.0
2017-06-05 00:00:50   0.20675   CR     7*60  19.23 0.16  21.1
2017-06-05 00:13:02   0.21885   CR    13*60  19.30 0.22  20.6

Photometry is based on nearby USNO-B1.0 stars (R2 magnitudes)
USNO-B.1_id    R2
0746-0830331 14.71
0746-0830367 14.76
0746-0830438 15.14
0746-0830455 14.77
0747-0821123 14.60

[GCN OPS NOTE(05jun17):  Per author's request, the duplicate text
of this circular was removed.]