TITLE:   GCN CIRCULAR
NUMBER:  31008
SUBJECT: GRB211023A: optical afterglow detection from Konkoly Observatory
DATE:    21/10/26 16:18:29 GMT
FROM:    Jozsef Vinko at Konkoly Observator  <vinko@konkoly.hu>

J. Vinko, A. Pal, L. Kriskovics, R. Szakats, K. Vida, Zs. Szabo
(Konkoly Observatory, Hungary) report:

We observed the field of GRB211023A (Fermi GBM team, GCN  30958)
with the RC80 robotic telescope at Piszkesteto Station of Konkoly
Observatory on 2021 Oct 25 starting at 17:46:47 UT. A series of 5x300 sec.
frames were collected through Sloan r'- and i' bands. The optical afterglow
(Zhirkov et al., GCN #30977;  Kann et al. GCN #30982; Hu et al. GCN #30990;
Belkin et al. GCN #31004)
was detected on the stacked frames with the following magnitudes, calibrated.
via nearby PS1 stars:

Date         UT-middle   t-T0(hr)  Exp(s)   r'(AB-mag)           i'(AB-mag)
2021-10-25   18:07:19    53.03     5x300    20.104 +/- 0.089  19.634 +/- 0.081

We measure the flux decline power-law index as -1.43 +/- 0.03, in accord with.
Belkin et al. (GCN #31004).