TITLE: GCN CIRCULAR NUMBER: 24223 SUBJECT: LIGO/Virgo S190425z: ZTF pre-merger limits on PS1 candidates DATE: 19/04/26 14:00:03 GMT FROM: Michael Coughlin at Caltech/LIGO Authors: Michael W. Coughlin (Caltech), Shreya Anand (Caltech), Tomas Ahumada (UMD) On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations We have analyzed the list of objects reported in Smith et al. (24210), and examined ZTF alerts for the same objects. We find that 7 of the events listed below have recent, previous detections with ZTF prior to the gravitational wave event trigger time and are likely unrelated to the BNS event S190425z (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN 24168). Name PS Name ZTF Name AT2019ebu PS19pp ZTF19aasbgll AT2019ebw PS19pq ZTF19aasazok AT2019ecc PS19pw ZTF19aapwgpg AT2019eck PS19qe ZTF19aapfrrw AT2019ecl PS19qg ZTF19aasgwnp AT2019ebr PS19qj ZTF18aaoxrvr AT2019ebo PS19qn ZTF19aarpgau ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; TTU USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert filtering and follow-up co-ordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019). -- Michael Coughlin David and Ellen Lee Prize Postdoctoral Fellow LIGO Laboratory West Bridge, Rm. 257 California Institute of Technology MC 100-36 Pasadena, CA 91125 email: mcoughli@ligo.caltech.edu website: http://www.michaelwcoughlin.com phone: +1 952 836 7113