TITLE: GCN CIRCULAR NUMBER: 10662 SUBJECT: Swift Trigger 420256: D50 optical limits DATE: 10/04/23 20:04:40 GMT FROM: Jan Strobl at AI AS CR,Ondrejov Jan Strobl (1), Martin Jelinek (2), Cyril Polasek (1), Petr Kubanek (2,3), Martin Nekola (1), Matus Kocka (1), Michal Jakubec (1) and Rene Hudec (1) (1. ASU AVCR Ondrejov, 2. IAA Granada, 3. GACE Valencia) We observed the field of Swift trigger 420256 (Hoversten et al., GCNC 10654) with the 0.5m telescope D50 in Ondrejov (Czech Republic), starting at 02:49:04 UT, i.e. 302s after the trigger. A sequence of 20s unfiltered images was obtained. We coadded 15x20s exposure, obtaining an image with a limitting magnitude Rc~18.0, with an effective exposure time 539s after the trigger. We do not detect any new source in combined or single images. This message can be cited.