[vsnet-grb-info 21100] GRB 180904A: SAO RAS optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23198
SUBJECT: GRB 180904A: SAO RAS optical observations
DATE:    18/09/05 00:46:37 GMT
FROM:    Moskvitin Alexander at SAO RAS  <mosk at sao.ru>

Moskvitin, A. S., Spiridonova O. I., Maslennikova O. A. (SAO RAS),
report on behalf of larger GRB follow-up team.

We observed the field of the GRB 180904A (D'Ai et al., GCNC 23194)
with the Zeiss-1000 telescope of SAO RAS (+ CCD UBVRcIc photometer)
on the 2018 September, 4.926 (mid. time).

The observations started since 7.2 minutes after the Swift trigger
(21:35:44--22:46:03 UT). 12 x 300 sec. exposures in Rc band
were obtained. We can not see any object inside the XRT enhanced
1".8 error circle (Osborne et al., GCNC 23196) down to
the limiting magnitude of R_lim = 22.7, but at the edge
of the circle we detected the object mentioned by Malesani et al.
(GCNC 23195). The preliminary magnitude of the object is
R = 21.9 +/- 0.2 (Vega system) compared to nearby USNO-B1 stars.

The finding chart can be found at
ftp://ftp.sao.ru/pub/grb/GRB/GRB180904A_SAORAS.png