TITLE:   GCN CIRCULAR
NUMBER:  29562
SUBJECT: GRB 210222B: VIRT optical detection
DATE:    21/02/24 04:10:56 GMT
FROM:    Priyadarshini Gokuldass at U. of the Virgin Islands  <priyadass.94@gmail.com>

P. Gokuldass (UVI), N. Orange (OrangeWave Innovative Science, LLC), R.
Strausbaugh (UVI), A. Cucchiara (UVI/College of Marin),
D. Morris (UVI) report:

We observed the field of GRB210222B (Gropp et al, GCN 29545) with the
0.5m Virgin Island Robotic Telescope (VIRT)
at the University of the Virgin Islands' Etelman Observatory on
02-23-2021 starting at 02:14:31 UT (T+3.6hrs).
We performed a series of exposures in R filter with a total exposure
of 4600 s. The weather conditions were clear
during the hours of observation with an average air masses as shown in
the table below.

We detect the optical transient reported by others (Gropp et al., GCN
29545, Hu et al., GCN 29546,Strausbaugh et al.,
GCN 29547, Mong et al., GCN 29548, Perley, GCN 29549, Aqui Fernandez
et al., GCN 29552, Lipunov et al., GCN 29554,
Jelinik et al., GCN 29557) at > 3-sigma confidence with magnitudes as
reported below:

T_mid       ||Exposure     ||Filter      ||Limit         ||Airmass
T+4.5 hrs   ||2000s        ||R           ||18.5 +/- 0.1  ||1.7
T+8.5 hrs   ||2600s	   ||R           ||20.0 +/- 0.2  ||1.5

The magnitude is estimated from comparison to nearby USNO B1 stars and
is not corrected for Galactic extinction.
Further analysis is in progress. The VIRT is still in the commissioning phase.

This work is supported by NASA-MUREP-MIRO grant NNX15AP95A, NSF EiR
AST Award 1901296, and NSF HBCU-UP AST Award 1831682.
This message can be cited.