TITLE:   GCN CIRCULAR
NUMBER:  31023
SUBJECT: GRB 211023A: 1.3m DFOT Optical Observations
DATE:    21/10/30 07:13:38 GMT
FROM:    Rahul Gupta at ARIES, India  <rahulbhu.c157@gmail.com>

[image: image.gif]Amit Kumar, Rahul Gupta, Amit Ror, Dimple, Ankur Ghosh, Arpan
Ghosh, Amar Aryan, Brajesh Kumar, S. B. Pandey, and Kuntal Misra (ARIES)
report:


We observed the Fermi GBM and LAT detected GRB 211023A (Fermi GBM
Team, GCN 30958; Lesage et al. 2021, GCN 30965; and N. Di Lalla et al.
2021, GCN 30961) with 1.3m Devasthal Fast Optical Telescope (DFOT)
located at Devasthal observatory of Aryabhatta Research Institute of
Observational Sciences (ARIES), India. The observations were started
on 2021-10-28 at 19:22:54 UT, i.e., ~ 5.26 days after the Fermi
trigger. We have taken multiple frames having an exposure time of 300
sec in the R filter. We clearly detected the optical afterglow of GRB
211023A (Lipunov et al. 2021, GCN 30970; Zhirkov et al. 2021, GCN
30977; Kann et al. 2021, GCN 30982; Hu et al. 2021, GCN 30990; Belkin
et al. 2021, GCN 31004, 31018, 31020; and Vinko et al. 2021, GCN
31008) in our stacked image. The preliminary photometric estimate of
the afterglow is the following :

Date Start UT   T-T0 (mid, days) Filter  Exp time (sec)   Magnitude

=========================================================
2021-10-28 19:22:54   ~5.28       R           300*15          21.37 +/- 0.08


Further observations are requested with 1.3m DFOT.The magnitude is not
corrected for the Galactic extinction in the direction of the burst.
Photometric calibration is performed using the standard stars from the
USNO-B1.0 catalog.

This circular may be cited.