GCN Circular 35172

N. Pankov (HSE, IKI),  A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI) report on behalf of GRB IKI FuN:

We observed the field 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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; Busman et al. GCN 35138
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; O'Connor et al., GCN 35139
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; Watson et al., GCN 35153
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, Kuin et al., GCN 35154
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; Dichiara  et al., GCN 35160
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; Fong et al., GCN 35163
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) with AZT-33IK telescope of Mondy observatory  in  R-filter on 2023-11-17, 2023-11-18 and 2023-11-20. Using image subtraction and the image on 2023-11-20 as a template we obtained preliminary photometry of the optical transient

Date       UT start  t-T0     Exp.   Filter   OT     Err.  
                   (mid, days)  (s)
2023-11-17 11:45:33  0.38349  30x120 R        21.00  0.16   
2023-11-18 12:09:46  1.41142  46x120 R        21.59  0.16  

The photometry is based on nearby USNO-B1.0 R2 stars. The index of power law (t-T0)^-alpha between  the two epochs is alpha = 0.8 (+0.13 -0.2).
However, photometry may be biased due to the template contamination by a still decaying optical transient, so we caution against using this index for any physical assessments.