TITLE: GCN CIRCULAR NUMBER: 36310 SUBJECT: LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility contuinued observations of S240422ed and candidate analysis DATE: 24/04/26 00:25:07 GMT FROM: Tomas Ahumada Mena at Caltech tahumada@caltech.edu
Tomas Ahumada (Caltech), Robert Stein (Caltech), Vishwajeet Swain (IITB), Anirudh Salgundi (IITB), Aswin Suresh (IITB), Gaurav Waratkar (IITB), Utkarsh Pathak (IITB), Eric Bellm (UW), Mansi Kasliwal (Caltech), Avery Wold (IPAC), Shreya Anand (Caltech), Viraj Karambelkar (Caltech), Theophile du Laz (Caltech), Simeon Reusch (DESY), Igor Andreoni (UMD), Varun Bhalerao (IITB), Brad Cenko (UMD), Michael Coughlin (UMN), David Kaplan (UWM), Jannis Necker (DESY), D. Perley (LJMU), Jesper Sollerman (OKC) report on behalf of the ZTF and GROWTH collaborations:
We continued observations of S240422ed (GCN 36236) 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). In total, we covered 59.6% (189.5 sq deg) of the reported localization region at least twice. Our observations were 300s, and reached a median depth of 19.2 in g-band, 19.7 in r-band and 20.3 in i-band. The detailed map of our coverage was reported to TreasureMap (Wyatt et al. 2020).
We queried the ZTF alert stream using Kowalski (Duev et al. 2019) through Fritz (Coughlin et al. 2023), 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 using the GAIA catalog), 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 ran forced photometry (FP) on ZTF images (Masci et al. 2019), requested ATLAS FP (Shingles et al. 2021), and require no detections before the LVK trigger.
We find no new candidate counterparts using ZTF data.
We also analyse candidate counterparts already reported by the Pan-STARRS and BlackGEM/MeerLICHT collaborations (GCN 36303 and GCN 36307):
TNS Name | Comment AT2024hfu | Also detected as ZTF24aakvqha, M~-18 mag (r-band) using NED photz = 0.092748. We confirm the lack of evolution in the r-band. AT2024hga | We find multiple ATLAS FP pre-detections (SNR 5-60) at the source location. There are no ZTF FP pre-detections in the last 12 months. AT2024hgb | We find multiple ATLAS FP pre-detections (SNR 4-50) at the source location. There are no ZTF FP pre-detections in the last 6 months. M~-19.8 mag (P1 z-band) using NED photz = 0.099940 (475 Mpc). AT2024hdl | We find multiple ATLAS FP pre-detections (SNR 4-120) at the source location. There are no ZTF FP pre-detections in the last 12 months. M~-17.3 mag (DECam z-band) using NED photz = 0.0552 (255 Mpc). AT2024hgc | ATLAS FP pre-detections (SNR 10-50). There are no ZTF FP pre-detections in the last 12 months. AT2024hfx | Also detected as ZTF21aawlmgc, there are multiple ATLAS and ZTF FP detections. Classified in PS1 STRM as QSO. AT2024hfo | ATLAS FP pre-detections (SNR 10-100). There are no ZTF FP pre-detections in the last 12 months. AT2024hft | Multiple ATLAS FP pre-detections (SNR 4-9). M~-18.9 mag (P1 z-band) using NED photz = 0.091 (430 Mpc). There are no ZTF FP pre-detections in the last 12 months. AT 2024hgl | Pre-detections in ATLAS FP (SNR 4-19, latest in 2024-01-07 and 2024-03-18), and in ZTF (2023-11-10).
We therefore disfavour all these candidates as potential counterparts.
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). The GROWTH India Telescope (GIT, Kumar et al., 2022) is set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. Its operations are partially supported by funding from the IIT Bombay alumni batch of 1994. The Fritz and SkyPortal projects acknowledge the generous support of The Gordon and Betty Moore Foundation.
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