B. O'Connor (CMU), I. Andreoni (JSI/UMD/NASA-GSFC), G. Srinivasaragavan (UMD), 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 performed additional 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 4-m Lowell Discovery Telescope (LDT) located in Flagstaff, AZ, under program M01 (PI: Andreoni). The observations began on 2023-11-20 02:50:02 UT (~3 d after the GRB) under seeing of ~2.2". We performed observations in the riz bands with 750 s exposure in each band.
At the location of the optical afterglow (Yang et al., GCN 35083; Rastinejad et al., GCN 35087; Gompertz et al., GCN 35088; Kumar et al., GCN 35089, Ahumada et al., GCN 35093; Andreoni et al., GCN 35099; Kilpatrick et al., GCN 35102; Chen et al., GCN 35105; Odeh et al., GCN 35118; Takahashi et al., GCN 35133; Schneider et al., GCN 35124; Busmann et al., GCN 35138), we clearly detect a source.
Preliminary photometry (including some contribution from the host) suggests fading by ~0.85 magnitudes in i-band from our previous observations obtained 2.0 days before (Andreoni et al., GCN 35099). Our observations confirm the fading of the optical afterglow candidate, as first reported by Fulton et al. (GCN 35121) and later by Busmann et al. (GCN 35138).
We thank the staff of the Lowell Observatory for their support during the observations.