TITLE: GCN CIRCULAR NUMBER: 16064 SUBJECT: GRB 140301A: Zadko observatory - Gingin optical observations DATE: 14/03/31 22:30:21 GMT FROM: Alain Klotz at IRAP-CNRS-OMP A. Klotz, D. Turpin (IRAP-CNRS-OMP), D. Macpherson (UWA/ICRAR), D. Coward (UWA), M. Boer, B. Gendre, K. Siellez, H. Dereli, O. Bardho (UNS-CNRS-OCA), A. Williams (PO-UWA), R. Martin (PO-UWA) report: We imaged the field of GRB 140301A detected by SWIFT (trigger 589590) with the Zadko robotic telescope (D=100cm) located at the observatory - Gingin, Australia. The observations started 70.7s after the GRB trigger (40.5s after the notice). The elevation of the field was at 26 degrees above horizon and weather conditions were good. Images were retrieved 30 days after their acquisitions due to a storage software problem. The first image is trailed with a duration of 60.0s (see the description in Klotz et al., 2006, A&A 451, L39). We do not detect any OT with a limiting magnitude of: t0+70.7s to t0+130.7s : Rlim = 18.4 The second image is 30.0s exposure in tracking mode: t0+159s to t0+189s : Rlim = 19.7 We co-added series of unfiltered exposures. The OT discovered by Kruehler et al. (GCNC 15899) is marginally detected 841 s (+/-255 s) after the trigger. More precisely the photometry is: =start= =end= 159 s 275 s CRlim = 21.8 289 s 465 s CRlim = 21.8 586 s 1096 s CR = 21.7 +/- 0.4 1217 s 1727 s CRlim = 21.9 This suggests this faint afterglow had culminated in brightness R=21.7 at t0+841s. Then it had declined to R=23.1 at t0+4.97h (Kruehler et al. GCN 15899) and to r'=23.8 at t0+11h (Elliott et al. GCNC 15904). This is compatible with a temporal decay of ~0.5. A photometry follow-up was performed with the Zadko telescope : =start= =end= 20.4 h 20.8 h CRlim = 22.2 All magnitudes were estimated with the nearby NOMAD1 stars and are not corrected for galactic dust extinction.