TITLE:   GCN CIRCULAR
NUMBER:  33538
SUBJECT: GRB 230328B: Liverpool Telescope afterglow detection
DATE:    23/03/29 16:01:52 GMT
FROM:    Ben Gompertz at U of Birmingham  <b.gompertz@bham.ac.uk>

B. P. Gompertz (U. Birmingham), D. B. Malesani (U. Radboud and DAWN/NBI) and A. J. Levan (U. Radboud) report:

We observed GRB 230328B (Fermi GBM Team, GCN 33526; Gropp et al., GCN 33527) with the IO:O optical camera on the 2m robotic Liverpool Telescope. Observations began on March 29, 2023 at 03:20:58 UT (~12.4 hr after the Fermi and Swift triggers) and consist of a series of 15x120 s exposures in each of the SDSS r' and i' filters.

We detect the optical afterglow first reported by Swift-UVOT (Gropp et al. GCN 33527) with the following magnitudes:

r' = 21.16 ± 0.06
i' = 20.75 ± 0.07

Magnitudes are in the AB system, calibrated against nearby PS1 stars (Chambers et al., 2016), and are not corrected for the Galactic reddening of E(B-V) = 0.06 magnitudes along the line of sight (Schlafly & Finkbeiner 2011).