TITLE: GCN CIRCULAR NUMBER: 21012 SUBJECT: Swift Trigger 748858: Zadko observatory - Gingin optical observations DATE: 17/04/19 13:33:13 GMT FROM: Alain Klotz at IRAP-CNRS-OMP A. Klotz, D. Turpin (IRAP-CNRS-OMP), D. Macpherson (UWA/ICRAR), D. Coward (UWA), M. Boer, (UNS-CNRS-OCA), Gendre B. (UVI - Etelman Obs.), A. Williams (PO-UWA), R. Martin (PO-UWA) report: We imaged the field of the trigger 748858 detected by SWIFT with the Zadko robotic telescope (D=100cm) located at the observatory - Gingin, Australia. The observations started 4.25h after the GRB trigger. The elevation of the field increased from 18 degrees above horizon and weather conditions were good. We co-added a two series of exposures: t0+4.25h to t0+4.40h : Rlim = 20.1 t0+4.65h to t0+5.22h : Rlim = 20.3 No source exhibit a variation flux compatible with a GRB afterglow. All sources detected by Zadko are presents in the DR9 SDSS-III image. Magnitudes were estimated with the nearby NOMAD1 stars and are not corrected for galactic dust extinction.