TITLE:   GCN CIRCULAR
NUMBER:  33426
SUBJECT: GRB 230228A: VIRT Optical Upper Limit
DATE:    23/03/08 21:15:43 GMT
FROM:    Priya Gokuldass at Florida Tech  <pgokuldass2020@my.fit.edu>

 K. Noonan (UVI), N. Orange (OrangeWave Innovative Science, LLC), P.
Gokuldass (Florida Tech), D. Morris (UVI), K. Smith (UVI), R. Querrard
(UVI) report:

We observed the field of GRB 230228A (Dichiara et al., GCN 33378) with
the 0.5m Virgin Island Robotic Telescope (VIRT) at the University of
the Virgin Islands' Etelman Observatory on 02-28-2023 starting at
23:29:41 UT (T+17.5 hrs). We performed a series of exposures in the R
filter with a total exposure of 2940s. The weather conditions were
clear during the hours of observation. The GRB was positioned at a
lower altitude with an average airmass of 2.7.

We detect no new source within the enhanced XRT position error circle
(Beardmore et al., GNC 33382) consistent with other non-detections
(Lim et al., GCN 33380, Lu et al., GCN 33381, Belkin et al., GCN
33383, Hu et al., GCN 33387, and Breeveld et al., GCN 33392) and
report the following 3-sigma upper limit:

T_mid            ||Exposure     ||Filter      ||Limit
T+ 18 hrs       ||2940s          ||R            ||>20.6

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

We acknowledge financial support from NASA MUREP MIRO award
80NSSC21M0001, NASA EPSCoR award 80NSSC22M0063, and NSF EiR award
1901296. R.Q. and N.B.O. also acknowledge financial support from South
Carolina Space Grant award 80NSSC20M0054. This message can be cited.