[vsnet-grb-info 27396] GRB 210204A (ZTF21aagwbjr/AT2021buv): continued CrAO and AbAO optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29499
SUBJECT: GRB 210204A (ZTF21aagwbjr/AT2021buv): continued CrAO and AbAO optical observations
DATE:    21/02/12 23:18:51 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

S. Belkin (IKI), A. Pozanenko (IKI), V. Rumyantsev (CrAO), R. Ya. 
Inasaridze (AbAO), N. Pankov (HSE) report on behalf of GRB IKI FuN:

We continued observation of the ZTF21aagwbjr/AT2021buv transient (Kool 
et al., GCN 29405) at the redshift of 0.876 (Xu et al., GCN 29432) which 
is  an afterglow (Kennea et al., GCN 29413; Teja  et al., GCN 29414; 
Belkin  et al., GCNs 29417, 29438;   Rossi et al., GCN 29433; Gupta et 
al., GCN 29490) of  GRB 210204A (Fermi GBM team, GCN 29390; Li et al., 
GCN 29392; Hurley et al., GCN 29408; Waratkar et al., GCN 29410; 
Frederiks et al., GCN 29415). Images in R-filter were taken with AS-32 
telescope of Abastumani observatory (AbAO) and  ZTSh 2.6m telescope of 
CrAO observatory on 2021-02-09 and 2021-02-11.

Preliminary photometry of the afterglow in combined images is following

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

2021-02-09 18:41:28 5.52572  R      25*120 21.09 0.08  22.6  ZTSh
2021-02-09 19:28:42 5.55610  R      43*60  21.4  0.2   22.5  AS-32
2021-02-11 18:18:20 7.50966  R      50*60  21.8  0.2   22.5  AS-32
2021-02-11 21:32:47 7.64817  R      30*120 21.6  0.3   21.8  ZTSh

The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
1014-0149033 15.43
1014-0149115 17.00

A light curve can be found in
http://grb.rssi.ru/GRB210204A/GRB210204A_lc.png

Our photometry confirms suggested jet-break (Rossi et al. GCN 29433; 
Gupta et al., GCN 29490).