GCN Circular 35138

Malte Busmann (LMU), Daniel Gruen (LMU),  Brendan O’Connor (CMU), Antonella Palmese (CMU), Lei Hu (CMU), Arno Riffeser (LMU/MPE), Ananya Shankar (LMU) report:

We observed 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 2m Fraunhofer telescope at Wendelstein Observatory, Germany. Observations were obtained using the 3kk imager in the r, i, and J bands simultaneously. The data were obtained starting at 2023-11-19 18:11:39 UT (~2.6 d after the GRB) under ~2” seeing. 

At the location of the optical transient (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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) we measure an optical brightness of 

r = 21.1 +/- 0.1 AB mag
i = 21.2 +/- 0.2 AB mag

Image subtraction has not yet been performed and these magnitudes encompass both the transient and host galaxy flux. These measurements are consistent with the archival host galaxy magnitudes, and confirm fading of the optical transient as reported by Fulton et al. (GCN 35121
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), solidifying the connection to the GRB.

The magnitudes are not corrected for Milky Way extinction and the photometry was calibrated against nearby stars in the PS1 catalog. 

We thank the staff of the Wendelstein Observatory for obtaining these observations.