TITLE:   GCN CIRCULAR
NUMBER:  33680
SUBJECT: GRB 230420A: Lowell Discovery Telescope Optical Detection
DATE:    23/04/24 17:00:41 GMT
FROM:    Brendan O'Connor at UMD <oconnorb@umd.edu>

B. O'Connor (UMD, GWU), E. Hammerstein (UMD), S.B. Cenko (UMD, NASA-GSFC), report on behalf of a larger collaboration:

We observed GRB 230420A (Klingler et al. GCN 33658) with the Large Monolithic Imager (LMI) on the 4.3m Lowell Discovery Telescope (LDT). Observations began on 2023-04-23 at 05:14:37 UT corresponding to ~2.8 d after the GRB trigger. Observations were carried out in r-band and i-band for 1800 s each at airmass 1.05 under seeing of ~1.6".

At the location of the optical counterpart (Hu et al. GCN 33663, Fu et al. GCN 33665, Fausey et al. GCN 33671) we detect a weak source in each filter. We measure magnitudes r~25.0+/-0.4 AB mag and i~24.2+/-0.2 AB mag. This is likely dominated by the contribution from the possible host galaxy  (Fausey et al. GCN 33671).

Magnitudes are calibrated against the PS1 catalog and are not corrected for Galactic extinction.

We thank the staff of the Lowell Discovery Telescope for assistance with these observations.