TITLE: GCN CIRCULAR NUMBER: 20109 SUBJECT: GRB 161023A: Zadko observatory - Gingin optical observations DATE: 16/10/24 14:28:37 GMT FROM: Alain Klotz at IRAP-CNRS-OMP Klotz A., Turpin D., Atteia J.L. (CNRS-OMP-IRAP), Boer, M., Laugier, R. (CNRS-ARTEMIS), Gendre B. (UVI - Etelman Obs.), Coward, D. McPherson, D. Williams A., Martin R., Moore J., Dodson R. (UWA) report: report: We imaged the field of GRB 161023A detected by Integral (trigger 7613, Mereghetti et al., GCN 20103) with the Zadko robotic telescope (D=100cm) located at the observatory - Gingin, Australia. The observations started 0.55 day after the GRB trigger. The elevation of the field decreased from 72 degrees above horizon and weather conditions were good. We detected the candidate couterpart mentioned by Gorbovskoy et al. (GCNC 20102) and Tanvir al. (GCN 20104). We used the same calibration star than Guidorzi et al. (GCNC 20107): t0+0.55d to t0+0.63d : R = 19.09 +/- 0.05 Magnitudes are not corrected for galactic dust extinction.