TITLE:   GCN CIRCULAR
NUMBER:  29950
SUBJECT: ZTF21aayokph (AT2021lfa): Assy optical observations
DATE:    21/05/06 16:17:11 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed the field of  ZTF21aayokph (AT2021lfa) (Yao et al., GCN 
29938) with AZT-20 telescope of Assy-Turgen observatory starting on 
2021-05-05 (UT) 15:51:00.

We clearly detect the optical transient (Yao et al., GCN 29938; Watson 
et al., GCN 29940; Butler et al., GCN 29941; Yao et al., GCN 29945; Fu 
  et al., GCN 29948).

Preliminary photometry of the optical transient  in r',i' - filters is 
following

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

2021-05-05 15:51:00  n/a        35*60   r'      21.20  0.06   22.5
2021-05-05 16:40:30  n/a        57*60   i'      20.83  0.06   21.8

The photometry is based on the nearby SDSS-DR12 stars.

We note the same color r'-i'= 0.37 +/- 0.08 of our observations and the 
color which can be deduced from RATIR observations r-i = 0.42 +/- 0.07 
at ~0.5 days earlier (Butler et al., GCN 29941).