TITLE: GCN CIRCULAR NUMBER: 39256 SUBJECT: LIGO/Virgo/KAGRA S250206dm: Observations from WINTER DATE: 25/02/09 20:04:26 GMT FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay karambelkarvraj21197@gmail.com
Robert Stein (JSI), Viraj Karambelkar (Caltech), Danielle Frostig (CfA), Mansi Kasliwal (Caltech), Nathan Lourie (MIT), Geoffrey Mo (MIT) and Robert Simcoe (MIT) report:
We observed the localization region of the S250206dm (GCN 39175, 39231) with the 1.2 sq. degree near-IR WINTER camera on the Palomar 1-m telescope (Lourie et al. 2021, Frostig et al. 2024) in J-band on two nights UTC 2025-02-08 and 2025-02-09. Our observations began at 2025-02-08 04:05 UTC, approximately 30.7 hours after the merger. Our observations covered a total of 23.8 sq. deg. of sky for which reference images were available, corresponding to 37% of the total probability. Of this, 14% was covered at least twice, while 23% was covered once and will be repeated tonight. Our observations reached a median depth of 18 mag AB.
The images were processed using the WINTER data reduction pipeline ( https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) using images from the UKIRT Hemisphere survey (Dye et al. 2018) as references for image subtraction. We search for WINTER sources with multiple detections, and for any WINTER source with a cross-match in the alert stream of the Zwicky Transient Facility (Bellm et al. 2019). We further remove stellar sources by cross-matching to Gaia, and we are left with no remaining transient candidates.
We also cross-match WINTER detections to the position of all 35 sources reported to TNS in the localisation of S250206dm since merger. We find no WINTER detections for any of these transients.
Further observations of the GW event are planned over the coming days. With more data, additional analysis can be performed to identify transients in sky regions without archival UKIRT coverage. This includes the area containing the candidate neutrino counterpart reported by IceCube (GCN 39176), for which initial WINTER data has been taken.
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
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