TITLE: GCN CIRCULAR NUMBER: 39229 SUBJECT: LIGO/Virgo/KAGRA S250206dm: Spectroscopic Classification of AT2025bay and AT2025baz with Keck I/LRIS DATE: 25/02/08 07:55:32 GMT FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay karambelkarvraj21197@gmail.com
Viraj Karambelkar (Caltech), Tomás Ahumada (Caltech), Mansi Kasliwal (Caltech) report on behalf of the ZTF and GROWTH collaborations:
We report optical spectroscopy of two counterpart candidates reported by the Zwicky Transient Facility, AT 2025bay, AT 2025baz (GCN #39228) in the localization region of LIGO/Virgo S200206dm (LVC, GCN #39175,39184). We used the Low Resolution Imaging Spectrometer (Oke et al. 1995) on the Keck I telescope, reduced data using the idl package lpipe (Perley 2019) and find:
ZTF25aaffyzc / AT2025bay shows broad features matching a Type Ia supernova before maximum at z = 0.19
ZTF25aaffzpx / AT2025baz matches a Cataclysmic Variable in the Milky Way and shows Balmer emission lines at z = 0.0
Thus, AT2025bay and AT2025baz are not related to the gravitational wave event.
We are grateful to the Keck Observatory staff, Sherry Yeh and Matthew Wahl, as well as observers, Andrew Howard and Howard Isaacson, for swiftly co-operating with these Target-of-Opportunity observations for rapidly setting targets.
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