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GCN Circular 33848

# LIGO/Virgo/KAGRA S230521k: Zwicky Transient Facility observations
2023-05-22T04:35:25Z (17 days ago)
Tomas Ahumada at U. of Maryland <>
Tomas Ahumada (CIT), Viraj Karambelkar (CIT), Robert Stein (CIT), Gaurav Waratkar (IITB), Anirudh Salgundi (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), report on behalf of the ZTF and GROWTH collaborations: We serendipitously observed the localization region of LVC trigger S230521k as part of routine Zwicky Transient Facility (ZTF; Graham et al., 2019; Bellm et al., 2019) survey operations. We obtained a total of 100 images covering g, r, and i bands for a total of 3810 seconds. These serendipitous observations covered 1238.8 square degrees beginning at 2023-05-21T05:32:51 (2 minutes after the burst trigger time) corresponding to ~9% 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), and AMPEL (Nordin et al. 2019). 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. Two sources passed our criteria and were inside the 95% error region: |----------------------------------------------------------------------------------------------------- | id | alias | ra | dec | mjd | mag±err (ab) | filter | |----------------------------------------------------------------------------------------------------- | ZTF23aaladzz | AT2023jcp | 275.9841 | 24.9580 | 60085.36780 | 20.18±0.17 | r | | ZTF23aaladoy | AT2016bqh/AT 2023jbu | 280.1828 | 27.0236 | 60085.36780 | 15.56±0.03 | g | |----------------------------------------------------------------------------------------------------- Forced photometry at the location of AT2023jcp detections 4 days prior to the GW event merger time. Thus, we rule out this source as a candidate counterpart. A source 0.1 arcsec from ZTF23aaladoy was previously reported to TNS in 2016, thus we rule it out as a viable candidate. 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.
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