TITLE:   GCN CIRCULAR
NUMBER:  29269
SUBJECT: GRB 210104A: iTelescope optical upper limit
DATE:    21/01/06 10:19:18 GMT
FROM:    Filipp Dmitrievich Romanov at Amateur astronomer  <filipp.romanov.27.04.1997@gmail.com>

I observed the field of GRB 210104A (Troja et al., GCN Circ. 29233)
with remote telescope T11 (0.50-m f/6.8 reflector + CCD + f/4.5 focal
reducer) of iTelescope.Net in New Mexico Observatory. Three images
with AstroDon Luminance filter and with 300 seconds exposure time were
obtained on 2021-01-05. Start time of exposures: 06:46:48 UT (~19.3 h.
after trigger; Binx1), 06:52:21 UT (Binx2) and 06:57:44 UT (Binx1). I
did not detect any optical transients (magnitude limit of about 21.0
in stacked image).