GCN Circular 35139

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
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; Navaneeth et al., GCN 35072
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; Beardmore et al., GCN3574
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; Cattaneo et al., GCN 35075
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; Svinkin et al., GCN 35079
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; Cheung et al., GCN 35081
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, Dafcikova et al., GCN 53095
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) 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
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; Rastinejad et al., GCN 35087
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; Gompertz et al., GCN 35088
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; Kumar et al., GCN 35089
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, Ahumada et al., GCN 35093
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; Andreoni et al., GCN 35099
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; Kilpatrick et al., GCN 35102
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; Chen et al., GCN 35105
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; Odeh et al., GCN 35118
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; Takahashi et al., GCN 35133
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; Schneider et al., GCN 35124
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; Busmann et al., GCN 35138
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), 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
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). Our observations confirm the fading of the optical afterglow candidate, as first reported by Fulton et al. (GCN 35121
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) and later by Busmann et al. (GCN 35138
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).

We thank the staff of the Lowell Observatory for their support during the observations.