TITLE: GCN CIRCULAR NUMBER: 39228 SUBJECT: LIGO/Virgo/KAGRA S250206dm: Candidates from the Zwicky Transient Facility DATE: 25/02/08 07:48:41 GMT FROM: Tomas Ahumada Mena at Caltech tahumada@caltech.edu
Tomás Ahumada (Caltech), Viraj Karambelkar (CIT), Eric Bellm (UW), Mansi Kasliwal (CIT), Shreya Anand (Stanford), Robert Stein (JSI/UMD), Theophile du Laz (CIT), Avery Wold (IPAC), Igor Andreoni (UMD), Varun Bhalerao (IITB), Brad Cenko (NASA GSFC/UMD), Michael Coughlin (UMN), David Kaplan (UWM), Leo Singer (NASA GSFC), Jesper Sollerman (OKC) report on behalf of the ZTF and GROWTH collaborations:
We observed the localization region of the LVK trigger S250206dm (GCN 39175) 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 39184). We started observations in the g- and r- beginning at 2024-02-08 02:21 UTC, approximately 29 hours after event time (delay due to wet weather at Palomar on the first night). We targeted 52% (1081 sq deg) of the reported localization region with 300s exposures.
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). 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), reject AGNs based on WISE colors, and apply machine learning algorithms for classification (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 on ZTF images (Masci et al. 2019) and required no detections before the LVK trigger.
Two sources were found within the 95% localization region and reported to TNS:
id | AT name |ra |dec | mjd| mag |filter| comment ZTF25aaffzpx | AT 2025baz | 02:19:26.60 | +47:32:49.80 | 60714.15932870 | 20.4 | r | hostless ZTF25aaffyzc | AT 2025bay | 00:30:01.17 | +37:10:06.06 | 60714.13770830 | 20.5 | r | no redshift available
Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. GROWTH acknowledges the generous support of the NSF under PIRE Grant No 1545949. 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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