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"