TITLE:   GCN CIRCULAR
NUMBER:  35182
SUBJECT: GRB230728A: VIRT optical upper limit
DATE:    23/11/24 20:38:00 GMT
FROM:    Priya Gokuldass at ERAU <gokuldap@my.erau.edu>

Kiwanee' Smith (UVI), P. Gokuldass (ERAU), N. Orange (OrangeWave Innovative Science, LLC), D. Morris (NASA), K. Noonan (UVI), R. Querrard (UVI), T. Lombardi (Eckerd College), Dylon Smith (UVI)

We observed the field of GRB230728A (Salvaggio et al., GCN 34282; Evans et al., GCN 34286) with the 0.5m Virgin Island Robotic Telescope (VIRT) at the University of the Virgin Islands' Etelman Observatory on 07-28-2023 starting at 04:22:27.816 (T+1.3 hrs). We performed a series of exposures in R filter with a total exposure of 1560s. The weather conditions were clear during the hours of observation with an average airmass of ~1.2. 

We do not detect any source within the enhanced XRT position (Evans et al., GCNC 34286). This non-detection is consistent with the upper limits reported by MASTER (Lipunov et al. GCNC 34281), NOT (Xu et al. GCNC 34285), UVOT (Oates et al. GCNC 34288), LCOGT (Strausbaugh et al. GCNC 34289) and BOOTES-1 (Hu et al. GCNC 34291). We report the following 3-sigma upper limit: 

T_mid        ||Exposure ||Filter ||Limit 
T+ 1.5 hrs ||1560s         ||R        ||>20.5

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.