TITLE:   GCN CIRCULAR
NUMBER:  30637
SUBJECT: GRB 210807A: continued Assy, AbAO and Mondy observations
DATE:    21/08/12 19:34:29 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

S. Belkin (IKI),  A. Pozanenko (IKI), V. Kim (FAI, Pulkovo Observatory), 
  R. Ya. Inasaridze (AbAO), E. Klunko (ISTP),  M. Krugov (FAI), N. 
Pankov (HSE),  D. Datashvili (AbAO), V. R. Ayvazian (AbAO),  G. V. 
Kapanadze (AbAO)  report on behalf of IKI GRB FuN:

We continued observation of the GRB 210807A (Lien et al., GCN 30600; 
Ripa  et al., GCN 30624) with AZT-20 of Assy observatory, AZT-33IK of 
Mondy observatory,  and AS-32 of Abastumani observatory.

The optical transient GRB 210807A (Lien et al., GCN 30600; Hu et al., 
GCN 30602; Lipunov et al., GCN 30607; Kim et al., GCNs 30614, 30616; 
LaPorte et al., GCN 30618; Schmidl et al., GCN 30628) was detected in 
almost all of our stacked images. Preliminary photometric results are 
presented below:

Date       UT start  t-T0     Filter Exp.   OT    Err.  UL(3sig) Observ.
                      (mid, days)        (s)
2021-08-07 23:46:09  0.58957   R     53*60  20.94 0.09 21.6    AbAO
2021-08-09 17:11:54  2.31822   R     30*120 22.6  0.35 22.5    Mondy
2021-08-10 17:22:17  3.32334   R     27*120 n/d   n/d  22.7    Mondy
2021-08-10 21:33:07  3.50135   r(AB) 65*60  23.14 0.26 23.7    Assy


The photometry is based on the nearby stars of the USNO-B1.0 catalog.
USNO-B1.0_id R2
1482-0188929 16.72
1482-0188954 15.47
1482-0189006 15.38

and based on the same stars presented in PS1 catalog for r(AB) calibrations.

The light curve plotted based on available data for can be found at

http://grb.rssi.ru/GRB210807A/GRB210807A_LC.png

The light curve can be approximated by broken power law with power law 
indices of -0.55 and -1.05 before and after break at about 0.22 days.