TITLE:   GCN CIRCULAR
NUMBER:  35099
SUBJECT: GRB 231117A: Lowell Discovery Telescope Observations
DATE:    23/11/18 17:18:44 GMT
FROM:    Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>

I. Andreoni (JSI/UMD/NASA-GSFC), G. Srinivasaragavan (UMD), B. O'Connor (CMU), T. Ahumada (Caltech), S. B. Cenko (NASA-GSFC), J. Durbak (UMD), E. Hammerstein (UMD), N. Klingler (UMBC/NASA-GSFC), A. Kutyrev (NASA-GSFC), L. Singer (NASA-GSFC), S. Veilleux (UMD):

We report target of opportunity follow-up observations of GRB 231117A (Laha et al., GCN 35071; Navaneeth et al., GCN 35072; Beardmore et al., GCN3574; Cattaneo et al., GCN 35075; Svinkin et al., GCN 35079; Cheung et al., GCN 35081, Dafcikova et al., GCN 53095) with the Large Monolithic Imager (LMI) mounted at the Lowell Discovery Telescope (LDT) located in Flagstaff, AZ, under program M01 (PI: Andreoni).

Observations started on 2023-11-18 at 01:46 UT (~22.7 hr after the GRB trigger). We obtained sets of 4x150s exposures for each g-r-i-z filter. The candidate afterglow identified by Yang et al.; GCN 35083 (also detected by Rastinejad et al., GCN 35087; Gompertz et al., GCN 35088; Kumar et al., GCN 35089, Ahumada et al., GCN 35093; Rhodes et al., GCN 35097) is well detected. Preliminary photometry of the images, with contribution from the host galaxy included and not corrected for Galactic extinction, was measured as follows in the AB magnitude system:

g = 20.55 +/- 0.04 mag
r = 20.20 +/- 0.04 mag
i = 20.05 +/- 0.04 mag
z = 19.98 +/- 0.03 mag

We thank Ben Shafransky and the Lowell Observatory staff for their support.