[vsnet-grb-info 28213] GRB 210610B: T-CAT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30316
SUBJECT: GRB 210610B: T-CAT optical observations
DATE:    21/06/25 14:40:15 GMT
FROM:    Denis Marchais at Amateur astronomer  <denis.marchais at free.fr>

I observed the field of GRB 210610B (Page et al., GCN #30170) with the
T-CAT telescope 0.4-meter f/4 Newton with a f/3 reducer, IR-cut filter
at 630nm and ZWO ASI533MC camera, located in Cintegabelle, France, on
June 11, 12 and 13.

The camera has a Sony sensor with Bayer filters R,G,B, that fairly 
match the standard Bc, Vc, and r' filters considering the additional
IR-cut filter. Each observation results from stacking 120x 32s exposures.

The GRB OT is clearly detected in the stacked frames at the following
location, matching other observations (e.g. , Fynho et al. GCN #30182,
Osborne et al. GCN #30186) though approaching the detection limit on
third observation, June 13th.
   RA(J2000)  = 16h 15m 40.39s
   Dec(J2000) = +14d 23' 56.3"

The following magnitudes were obtained thanks to PixInsight photometric 
calibration using nearby APASS DR10 stars.

Date        UT start     Filter   Exp. (s)    OT     err
2021-06-11  23:52:21     Bc       120x 32     20.53  +/- 0.05
2021-06-11  23:52:21     Vc       120x 32     20.00  +/- 0.04
2021-06-11  23:52:21     r'       120x 32     19.64  +/- 0.04
2021-06-12  22:48:22     Bc       120x 32     21.79  +/- 0.11
2021-06-12  22:48:22     Vc       120x 32     20.91  +/- 0.07
2021-06-12  22:48:22     r'       120x 32     20.90  +/- 0.10
2021-06-13  22:45:36     Bc       120x 32     21.77  +/- 0.1
2021-06-13  22:45:36     Vc       120x 32     21.42  +/- 0.09
2021-06-13  22:45:36     r'       120x 32     21.76  +/- 0.2

I thank A. Taylor, H.-B. Eggenstein and E. Broens (GCN#30205) for sharing
information through the KNCatcher citizen-science programme initiated by
S. Antier and A. Klotz as part of GRANDMA initiative (GRANDMA Observations
of Advanced LIGO's and Advanced Virgo's Third Observational Campaign,
Antier et al. https://arxiv.org/abs/2004.04277v2).