Tomas Ahumada (CIT), Igor Andreoni (UMD), Akash Anumarlapudi (UWM), Viraj Karambelkar (CIT), Harsh Kumar (IITB), Theophile du Laz (CIT), Simeon Reusch (DESY), Anirudh Salgundi (IITB), Robert Stein (CIT), Vishwajeet Swain (IITB), Gaurav Waratkar (IITB), Shreya Anand (CIT), Eric Bellm (UW), Varun Bhalerao (IITB), Brad Cenko (UMD), Michael Coughlin (UMN), Brian Healy (UMN), David Kaplan (UWM), Mansi Kasliwal (CIT), Jannis Necker (DESY), D. Perley (LJMU), Avery Wold (IPAC) report on behalf of the ZTF and GROWTH collaborations:
We reobserved the localization region of the LVK trigger S230627c (GCN 34086) with the Palomar 48-inch telescope equipped with the 47 square-degree Zwicky Transient Facility (ZTF) camera (Graham et al., 2019; Bellm et al., 2019). We obtained images in the g- and r-bands of the Bilby map (GCN 34087) beginning at ~26.2 hours after the LVK trigger time, covering 78.6% (106.2 sq deg) of the probability enclosed in the localization region.
We queried the ZTF alert stream using AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019) through Fritz (Coughlin et al. 2023), and emgwcave (Karambelkar et al. in prep). We required at least 2 detections separated by at least 15 minutes to select against moving objects. Furthermore, we cross-match our candidates with the Minor Planet Center to flag known asteroids, reject stellar sources (Tachibana and Miller 2018), and apply machine learning algorithms (Mahabal et al. 2019). We require that no spatially coincident ZTF alerts were issued before the detection time of the LVK trigger. We also run forced photometry on ZTF images (Masci et al. 2019) and ATLAS images (Tonry et al. 2018, Smith et al. 2020) and require no 3- and 5-sigma detections before the LVK trigger respectively.
Our observations yielded no new candidates. Furthermore, the candidates circulated on our initial GCN 34089 (Anumarlapudi et al.) show a flat evolution.
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 the 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). Fritz and SkyPortal acknowledge the generous support of The Gordon and Betty Moore Foundation, through the Data-Driven Investigator Program.