TITLE:   GCN CIRCULAR
NUMBER:  29255
SUBJECT: GRB 210104B: Assy optical upper limit
DATE:    21/01/05 08:34:20 GMT
FROM:    Yerlan Aimuratov at Fesenkov Astrophysical Inst.(FAI)  <aimuratov@aphi.kz>

V. Kim (FAI, Pulkovo), I. Reva (FAI), M. Krugov (FAI), Y. Aimuratov 
(FAI) report:

We observed the field of GRB 210104B (Laha et al., GCN 29243) with 
AZT-20 1.5-m telescope
of Assy-Turgen Observatory (Assy) starting on Jan. 04 (UT) 22:31:15.
We did not find any optical counterpart in our 20x60s stacked image in 
the enhanced
XRT position (Evans et al., GCN 29253) down to an upper limit R~23.2
(see also Hu et al., GCN 29249 and Fu et al., GCN 29250).
Preliminary photometry of the filed is the following:

Date        UT start  t-T0         Filter  Exp.    OT    Err.  
UL(3-sigma) FWHM
                       (mid, days)          (s)                           
   (")
2021-01-04  22:31:15  0.06325      r'      20*60   n/d   n/d   23.2      
   2.3

Further observations on this object are not planned except personal 
request.