TITLE: GCN CIRCULAR NUMBER: 33900 SUBJECT: LIGO/Virgo/KAGRA S230529ay: Zwicky Transient Facility observations DATE: 23/05/31 03:32:40 GMT FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay karambelkarvraj21197@gmail.com

Viraj Karambelkar (CIT), Tomas Ahumada (CIT), Robert Stein (CIT), Akash Anumarlapudi (UWM), Gaurav Waratkar (IITB), Harsh Kumar (IITB), Anirudh Salgundi (IITB), Vishwajeet Swain (IITB), Theophile du Laz (CIT), Igor Andreoni (UMD), Michael Coughlin (UMN), Mansi Kasliwal (CIT), Varun Bhalerao (IITB), Simeon Reusch (DESY), Jannis Necker (DESY), Shreya Anand (CIT), Eric Bellm (UW), Brian Healy (UMN), S. B. Cenko (UMD), D. Kaplan (UWM), D. Perley (LJMU) report on behalf of the ZTF and GROWTH collaborations:

We observed the localization region of the LVC trigger S230529ay as part of routine Zwicky Transient Facility (ZTF; Graham et al., 2019; Bellm et al., 2019) survey operations. We obtained images in the r, i, and g bands beginning at 2023-05-30T04:13:34.003 UT (10 hours after the LVC trigger time), covering ~7% of the probability enclosed in the localization region.

We queried the ZTF alert stream using Kowalski (Duev et al. 2019) through Fritz (Coughlin et al. 2023) and emgwcave (Karambelkar et al. in prep), AMPEL (Nordin et al. 2019), and ZTFReST (Andreoni & Coughlin et al., 2021). 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 LVC 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 detections before the LVC trigger.

One source passed our criteria and is inside the 95% error region:

|----------------------------------------------------------------------------------------------------- | id | alias | ra | dec | mjd | mag±err (ab) | filter | |----------------------------------------------------------------------------------------------------- | ZTF23aamnpce | AT2023jtt | 235.9839 | 15.2248 | 60094.23830 | 20.49±0.23 | r | |-----------------------------------------------------------------------------------------------------

AT2023jtt is 0.5" from a galaxy that has a photometric redshift of photoz=0.22±0.06 from the Legacy Survey DR8 (Duncan, 2022), suggesting that it is probably not associated with the LVC trigger.

Further follow-up of this localization region will continue as part of regular survey operations.

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). GROWTH India telescope is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). GROWTH-India project is supported by SERB and administered by IUSSTF, under grant number IUSSTF/PIRE Program/GROWTH/2015-16 and IUCAA.