TITLE:   GCN CIRCULAR
NUMBER:  30205
SUBJECT: GRB 210610B: optical afterglow observations
DATE:    21/06/11 17:14:07 GMT
FROM:    Paul Vreeswijk at Radboud U/Nijmegen  <p.vreeswijk@astro.ru.nl>

P.M. Vreeswijk (Radboud) reports on behalf of E. Broens (Mol, Belgium):

���I observed the field of GRB 210610B (Page et al., GCN 30170; Kumar et
al., GCN 30174; Rumyantsev et al., GCN 30175; Hu et al., GCN 30177; de
Wet et al., GCN 30180; Romanov et al., GCN 30181, GCN 30182; Fynbo et
al, GCN 30182; Moskvitin, GCN 30187) using a 0.28-meter f7 SCT
telescope with a Moravian G2-1600 CCD camera and Astrodon
Johnson-Cousins BVRcIc filters.
 
Five 180 s exposures were average combined for each filter. In the B
filter the OT was only marginally detected with a SNR ~3.  The
following magnitudes were measured using eight APASS DR9 stars in the
field. The APASS DR9 r��� and i��� magnitudes were transformed to Rc and
Ic using the Jester et al. (2009, AJ 130, 873) relations.
 
2021-06-10  23:50:30 UT  Rc  17.20 +/- 0.07
2021-06-11  00:05:37 UT  V   17.74 +/- 0.09
2021-06-11  00:20:20 UT  Ic  16.8  +/- 0.2
2021-06-11  00:36:00 UT  B   18.4  +/- 0.2
2021-06-11  00:51:50 UT  Rc  17.25 +/- 0.08
2021-06-11  01:06:23 UT  V   17.71 +/- 0.09"