GCN Circular 29901

S. Belkin (IKI), V. Kim (FAI, Pulkovo Observatory), M. Krugov (FAI), A. 
Pozanenko (IKI),  N. Pankov (HSE, IKI) report on behalf of GRB IKI FuN:

We observed the field of  GRB 210420B (Moss et al., GCN 29833
Not found
 
 
; Lien et 
al., GCN 29854
Not found
 
 
; Osborne et al. GCN 29876
Not found
 
 
; Stamatikos et al., GCN29879
Not found
 
 
) 
with AZT-20 telescope of Assy-Turgen observatory starting on 2021-04-23 
(UT) 18:39:00.

We marginally detect the optical afterglow  (Lipunov et al., GCN 29845
Not found
 
 
; 
Oksanen et al., GCN 29846
Not found
 
 
; Hu et al., GCN 29847
Not found
 
 
; Tianrui Sun et al., GCN 
29848
Not found
 
 
; Leonini et al., GCN 29851
Not found
 
 
; de Ugarte Postigo et al., GCN 29852
Not found
 
 
, 
29853
Not found
 
 
; Watson et al., GCN 29858
Not found
 
 
; Zheng et al., GCN 29861
Not found
 
 
; Breeveld et 
al., GCN 29862
Not found
 
 
; Stecklum et al., GCN 29863
Not found
 
 
; Butler et al.,GCN 29864
Not found
 
 
; 
Jelinek et al., GCN 29866
Not found
 
 
; Watson, GCN 29867
Not found
 
 
; Leonini et al., GCN 29872
Not found
 
 
; 
Guelbenzu et al., GCN 29890
Not found
 
 
; Pankov et al., GCN 29894
Not found
 
 
; Ibrahimov et al., 
GCN 29895
Not found
 
 
).

Preliminary photometry of the source (afterglow or afterglow + host 
galaxy)  is following

Date       UT start  t-T0       Exp.    Filter  OT    Err.  UL(3sigma)
                     (mid, days)  (s)

2021-04-23 18:39:00  2.98478    113*60  r'      23.2  0.3   23.3

The photometry is based on the nearby SDSS-DR12 stars
RA DEC r
16:56:42.09384 +42:38:35.9628 15.541
16:57:24.93456 +42:34:14.6388 16.642
16:56:58.03392 +42:33:40.5468 16.987