TITLE:   GCN CIRCULAR
NUMBER:  30263
SUBJECT: GRB 210619B: Ondrejov D50 detection
DATE:    21/06/20 02:47:13 GMT
FROM:    Martin Jelinek at Astro.Inst-AVCR,Ondrejov  <martin.jelinek@asu.cas.cz>

M. Jelinek, J. Strobl, R. Hudec, C. Polasek (ASU CAS Ondrejov)
report:

We observed the position of the bright GRB 210420B (D'Avanzo et al., GCN
30261) with the D50 telescope of the Astronomical Institute Ondrejov, near
Prague, Czech Republic. We performed a series of unfiltered exposures
starting 23:59:53 UT, between 28 s and 2 h after the trigger.

The optical afterglow (Lipunov et al., GCNC30259 & 30262) is clearly
detected in single images. We can confirm a decaying nature of the object -
the afterglow faded to r'(AB)~17.7 mag during the course of our
observations, which were ended by twillight 2.0h after the trigger. The
alpha decay by the  end of observations was ~0.6, indicating a possible
plateau phase.