[vsnet-grb-info 24466] GRB 191221B: iTelescope optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26565
SUBJECT: GRB 191221B: iTelescope optical observations
DATE:    19/12/23 00:21:24 GMT
FROM:    Filipp Dmitrievich Romanov at Amateur astronomer  <filipp.romanov.27.04.1997 at gmail.com>

I observed the optical afterglow of GRB 191221B (Laha et al., GCN Circ.
26534) with remote telescope T32 (0.43-m f/6.8 reflector + FLI Proline
16803 CCD) of iTelescope.Net in Siding Spring Observatory (Australia) on
2019-12-22 since 13:28:52 UT (~16.8 hours after the trigger). Two images
were obtained in each band with Astrodon luminance filter and
Johnson/Cousins V filter for 180 and 120 seconds (Binx2). I detected the
optical afterglow in three images in the enhanced Swift-XRT position
(Beardmore et al., GCN Circ. 26540); it not present in images from DSS
Plate Finder.

The following magnitudes (mag. error ~ 0.2) were measured from comparison
to nearby stars from APASS DR9 catalogue (Henden et al., 2016):

Time of start  Exp.time  Mag.   Comp.star band  Filter
----------------------------------------------------------
13:28:52 UT    180 s     18.1        r'         Luminance
13:32:58 UT    180 s     18.3        V          V
13:36:51 UT    120 s     18.3        r'         Luminance
13:39:46 UT    120 s     <17.9       V          V
----------------------------------------------------------

Magnitudes were not corrected for Galactic extinction.