TITLE:   GCN CIRCULAR
NUMBER:  35292
SUBJECT: GRB 231205B: Ondrejov D50 optical upper limit
DATE:    23/12/06 18:45:19 GMT
FROM:    Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>

Alzbeta Malenakova, Martin Jelinek, Jan Strobl,  Rene Hudec,
Cyril Polasek (ASU CAS Ondrejov, CZ),
and Sergey Karpov (Institute of Physics, Prague, CZ)

report:

The 50 cm robotic telescope D50 located at Ondrejov
observatory (Czech Republic) reacted robotically to the
Swift-BAT alert of GRB 231205B (Evans et al., GCNC 35269),
reported also by GECAM-B (Liu et al., GCNC 35279), obtaining a
series of 20 s unfiltered images starting at 16:45:46 UT, i.e.
107 s post trigger.

We do not detect any new optical source in the XRT error box
(neither any new or strongly variable source in the BAT
errorbox) in single images (detection limit r' > 18.7) nor in
a combined 30 x 20 s frame (mean exp time 290 s post trigger,
with a limit r' > 21.0) similarly to Odeh et al. (GCNC 35270),
Jiang et al.  (GCNC 35280), Jiang et al. (GCNC 35281) and
Komesh et al. (GCNC 35287).  All magnitudes are calibrated
with Atlas Refcat 2.0 (Tonry et al., ApJ 867, 105, 2018).