[vsnet-grb-info 27183] GRB 210104A: Mondy optical observations, light curve

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29286
SUBJECT: GRB 210104A: Mondy optical observations, light curve
DATE:    21/01/10 22:34:47 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

S. Belkin (IKI), A. Pozanenko (IKI),  E. Klunko (ISTP), V. Kim (FAI, 
Pulkovo Observatory), Y. Aimuratov (FAI), M. Krugov (FAI) report on 
behalf of GRB IKI FuN:

We observed  GRB 210104A (Fermi GBM team, GCN 29232; Troja et al., GCN 
29233; Frederiks et al., GCN  29258; Cherry et al., GCN 29268) with 
AZT-33IK telescope of Sayan observatory (Mondy).   We detect the optical 
afterglow (Troja et al., GCN 29233; Xin et al., GCN 29235; Hu et al., 
GCN 29236; Hosokawa et al., GCN  29237; Kim et al., GCN 29238, 29265; 
Lipunov et al., GCN 29239; Horiuchi et al., GCN 29241; Breeveld et al., 
GCN 29247; Zhu et al., GCN 29252; Paek  et al., GCN 29254; Kumar et al., 
GCN 29257; Smartt et al., GCN 29262; Romanov, GCN 29269; Anandagoda et 
al., GCN 29273; Gokuldass, GCN 29274; Mao et al.,  GCN 29275; Moskvitin 
et al., GCN 29277).

Preliminary photometry of the afterglow  is following

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

2021-01-07 15:10:23   3.19681  R      80*90   n/d     n/d 22.1
2021-01-08 15:22:18   4.20438  R      59*120  22.2    0.2 22.9
2021-01-09 11:51:54   5.07980  R      90*120  22.7    0.3 22.7


The photometry is based on nearby stars of  USNO-B1.0
USNO-B1.0_id R2
1546-0139059 15.53
1546-0139029 14.82

A light curve of the afterglow based on our observations including 
reported early (Kim et al., GCN 29238, 29265, 29283) can be found in

http://grb.rssi.ru/GRB210104A/GRB210104A_LC.png