TITLE:   GCN CIRCULAR
NUMBER:  33717
SUBJECT: GRB 230420A: AROMA-N Optical Upper Limit
DATE:    23/05/02 09:00:50 GMT
FROM:    Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>

Y. Koyanagi, T. Sakamoto (AGU)

We observed the field of GRB 230420A detected by Swift
(Klingler et al., GCN Circ. 33658) with the 14-inch AGU Robotic
Optical Monitor for Astrophysical object - Narrow (AROMA-N)
located at the Sagamihara campus of Aoyama Gakuin University.

13 images of 60 sec exposures were taken in the R filter
starting from April 20 11:41:42 (UT) about 1.37 hours
after the trigger and stopped on April 20 11:59:16 (UT).
We do not detect the optical afterglow both in the individual
images and the stacked image.  The estimated five sigma
upper limit of the combined image (total exposure of 780 sec)
is ~17.1 mag using the USNO-B1 catalog.