Simeon Reusch (DESY), Tomas Ahumada (CIT), Anirudh Salgundi (IITB), Gokul Srinivasaragavan (UMD), Michael Coughlin (UMN), Vishwajeet Swain (IITB), Theophile du Laz (CIT), Jacob Wise (LJMU), Shreya Anand (CIT), Igor Andreoni (UMD), Eric Bellm (UW), Varun Bhalerao (IITB), S. Bradley Cenko (NASA/GSFC), Brian Healy (UMN), Mansi Kasliwal (CIT), Viraj Karambelkar (CIT), D. Kaplan (UWM), Harsh Kumar (IITB), Jannis Necker (DESY), Daniel Perley (LJMU), Robert Stein (CIT), Avery Wold (CIT/IPAC) report on behalf of the ZTF and GROWTH collaborations:
We observed parts of the localization region of LVK trigger S230516az as part of routine Zwicky Transient Facility (ZTF; Graham et al., 2019; Bellm et al., 2019) survey operations prior to and after merger time.
Following the GOTO GCN notice (Gompertz et al., 33979), we obtained forced photometry of GOTO23hu and detected the transient in the i-band with 20.14 mag (AB) at 2023-06-15 04:37:55 UT, roughly 13 hours prior to merger time. Furthermore, the transient has since then continued to brighten in the i- and g-band, rising 1.4 mag in the g-band within 4 days.
We thereby rule out GOTO23hu as potential counterpart to S230516az.
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; Tokyo Tech, Japan; IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA 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 database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019).