TITLE: GCN CIRCULAR NUMBER: 21744 SUBJECT: LIGO/Virgo G298048: Zadko Telescope 7 day observations of the OT candidate SSS17a/DLT17ck DATE: 17/08/29 08:29:39 GMT FROM: Eric Howell at U of Western Australia D. Coward (UWA), E. Howell (UWA), R. Laugier (ARTEMIS - CNRS/UCA/OCA), A. Klotz (IRAP - CNRS/UPS), M. Boer, (ARTEMIS - CNRS/UCA/OCA), I. Andreoni (Swinburne), J. Cook (Swinburne), D. Macpherson (UWA), J. Moore (UWA) and A. Burrell (UWA) report on behalf of OzGrav and TZAC (see acknowledgements below): We report 7 days of Zadko Telescope imaging of the transient SSS17a/DLT17ck in NGC4339 started on 2017-08-19 10:57 UT (t0+2 days). We use the stacked image of the night 201-08-26 (t0+9 days) as a mask to substract the light contribution from the galaxy NGC 4993 and synthesise one residual image for each nights observation. Photometry is performed using the star NOMAD-1 0666-0296321 for PSF fitting. The complete log of Zadko image analysis from t0+2 – t0+9 is: Tstart Tend r(AB) 1sigma 1.928 1.930 18.46 0.17 2.929 2.950 19.18 0.12 3.941 3.974 19.86 0.21 4.955 4.964 20.20 0.23 5.953 5.973 >20.6 6.958 6.978 >20.6 7.955 7.976 >20.6 Observations are compatible with a power law decay (alpha=-2) or with a exponential decay with a half time of 1.25 days. The Zadko Telescope is operated by the University of Western Australia (UWA), and was made possible by a philanthropic donation by James Zadko, to UWA. Zadko Telescope receives support from the ARC Centre of Excellence “OzGrav” for gravitational wave follow-up and discovery. The facility is managed by D.Coward (Director-UWA), E. Howell (UWA), J. Moore (UWA), A. Burrel (UWA), A. Greensky, J. Kennewell with collaborators I. Andreoni and J. Cook (Swinburne) This observation report was done in partnership with the LIGO follow-up collaboration TZAC, which is supported by M. Boer, A. Klotz, R. Laugier, K. Noysena