TITLE:   GCN CIRCULAR
NUMBER:  24708
SUBJECT: GRB 190530A: SAO RAS optical observations
DATE:    19/06/01 12:21:26 GMT
FROM:    Moskvitin Alexander at SAO RAS  <mosk@sao.ru>

Moskvitin A. S. and Uklein R. I. (SAO RAS)
report on behalf of larger collaboration.

We observed the field of the GRB 190530A (Fermi GBM Team, GCNC 24676;
Longo et al., GCNC 24679) with the 1-m telescope of SAO RAS
equipped with the MMPP (Multi-Mode Photometer-Polarimeter)
and UBVRcIc filters on May 31 / June 1 night.

We obtained 11 x 300 sec. frames in Rc band.
The OT (Lipunov et al., GCNC 24680; Kann et al., GCNC 24684;
Heintz et al., GCNC 24686; Izzo et al., GCNC 24687;
Xin et al., GCNC 24688; Watson et al., GCNC 24690;
Lipunov et al., GCNC 24693; Xin et al., GCNC 24697;
Belkin et al.,  GCNC 24698; Kann et al., GCNC 24700;
Siegel, GCNC 24703) is clearly detected in our stacked image.
The OT brightness is R(AB) = 19.39 +/- 0.05 (T_mid - T0 = 1.353 days).

The OT magnitude was calculated against the nearby SDSS stars
whose magnitudes were transformed with the equations of Lupton (2005).
The magnitude of OT was converted to AB system
and was not corrected for the Galactic extinction.