{
  "eventId": "LIGO/Virgo/KAGRA S230521k",
  "version": 2,
  "editedOn": 1722438469136,
  "submitter": "Tomas Ahumada at U. of Maryland <tahumada@astro.umd.edu>",
  "editedBy": "Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov>",
  "body": "Tomas Ahumada (CIT), Viraj Karambelkar (CIT), Robert Stein (CIT), Gaurav\nWaratkar (IITB), Anirudh Salgundi (IITB), Theophile du Laz (CIT), Igor\nAndreoni (UMD), Michael Coughlin (UMN), Mansi Kasliwal (CIT), Varun\nBhalerao (IITB), Simeon Reusch (DESY), Jannis Necker (DESY), Shreya Anand\n(CIT), report on behalf of the ZTF and GROWTH collaborations:\n\n\nWe serendipitously observed the localization region of LVC trigger S230521k\nas part of routine Zwicky Transient Facility (ZTF; Graham et al., 2019;\nBellm et al., 2019) survey operations. We obtained a total of 100 images\ncovering g, r, and i bands for a total of 3810 seconds. These serendipitous\nobservations covered 1238.8 square degrees beginning at 2023-05-21T05:32:51\n(2 minutes after the burst trigger time) corresponding to ~9% of the\nprobability enclosed in the localization region.\n\nWe queried the ZTF alert stream using Kowalski (Duev et al. 2019) through\nFritz (Coughlin et al. 2023) and emgwcave (Karambelkar et al. in prep), and\nAMPEL (Nordin et al. 2019). We required at least 2 detections separated by\nat least 15 minutes to select against moving objects. Furthermore, we\ncross-match our candidates with the Minor Planet Center to flag known\nasteroids, reject stellar sources (Tachibana and Miller 2018), and apply\nmachine learning algorithms (Mahabal et al. 2019). We require that no\nspatially coincident ZTF alerts were issued before the detection time of\nthe LVC trigger.\n\nTwo sources passed our criteria and were inside the 95% error region:\n\n|-----------------------------------------------------------------------------------------------------\n| id           | alias                |       ra |     dec |        mjd  |\nmag±err (ab)   | filter   |\n|-----------------------------------------------------------------------------------------------------\n| ZTF23aaladzz | AT2023jcp            | 275.9841 | 24.9580 | 60085.36780 |\n20.18±0.17     | r        |\n| ZTF23aaladoy | AT2016bqh/AT 2023jbu | 280.1828 | 27.0236 | 60085.36780 |\n15.56±0.03     | g        |\n|-----------------------------------------------------------------------------------------------------\n\n\nForced photometry at the location of AT2023jcp detections 4 days prior to\nthe GW event merger time. Thus, we rule out this source as a candidate\ncounterpart. A source 0.1 arcsec from ZTF23aaladoy was previously reported\nto TNS in 2016, thus we rule it out as a viable candidate.\n\nFurther follow-up of this localization region will continue as part of\nregular survey operations.\n\n\nZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC,\nUSA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY,\nGermany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan;\nIITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia.\nZTF acknowledges the generous support of the NSF under AST MSIP Grant No\n1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant\nNo 1545949. Alert distribution service provided by DIRAC@UW (Patterson et\nal. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019)\nand Kowalski (Duev et al. 2019). GROWTH India telescope is located at the\nIndian Astronomical Observatory (Hanle), operated by the Indian Institute\nof Astrophysics (IIA). GROWTH-India project is supported by SERB and\nadministered by IUSSTF, under grant number IUSSTF/PIRE\nProgram/GROWTH/2015-16 and IUCAA.\n",
  "format": "text/plain",
  "bibcode": "2023GCN.33848....1A",
  "circularId": 33848,
  "createdOn": 1684730125231,
  "subject": "LIGO/Virgo/KAGRA S230521k: Zwicky Transient Facility observations"
}