TITLE:   GCN CIRCULAR
NUMBER:  30934
SUBJECT: GRB 210919A: LDT optical observations and candidate host galaxies
DATE:    21/10/12 23:14:30 GMT
FROM:    Brendan O'Connor at UMD  <oconnorb@umd.edu>

B. O'Connor (UMD, GWU),E. Hammerstein (UMD),S.B. Cenko (UMD,
NASA-GSFC),E. Troja (UMD, NASA-GSFC),A.Gottlieb (UMD,
NASA-GSFC),S.Dichiara (PSU),A. Kutyrev (UMD,NASA-GSFC),
S. Veilleux (UMD)

We observed the field of GRB 210919A (Tohuvavohu et al., GCN 30846)
using the Large Monolithic Imager (LMI) on the 4.3m Lowell Discovery
Telescope (LDT) at Happy Jack, AZ. Observations started on October 11,
2021 at 11:39:44 UT (~3 weeks after the GRB trigger), and were carried
out in r-band for 5x300 s exposures. The observations were performed at
airmass 1.2 with seeing 0.8".

At the position of the optical source reported by Kann et al.
(GCNs 30883 and 30884) we do not detect any source down to a
3-sigma upper limit of r>25.1 AB mag. However, within the XRT
enhanced position (Goad et al., GCN 30850), we detect a source
with magnitude r~24.0+/-0.1 AB mag at position
RA, DEC = 05:21:00.87,+01:18:42.68 +/- 0.5",
which is 3.4" offset from the Kann et al. source (GCNs 30883 and 30884).

The source appears marginally extended although it cannot be
confidently associated with GRB 210919A due to the high probability
of chance coincidence of Pcc=0.45 (Bloom et al. 2002). We also note
the presence of a bright galaxy (also seen in SDSS)
with r~20.47+/-0.05 mag at an offset of ~13" from the XRT localization.
This galaxy has a photometric redshift z~0.27+/-0.12, and probability
of chance coincidence is Pcc=0.15.

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

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