TITLE: GCN CIRCULAR NUMBER: 39273 SUBJECT: LIGO/VIRGO/KAGRA S250206dm: AT 2025bbo spectroscopic observations with NIRES on Keck II DATE: 25/02/11 01:04:26 GMT FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay karambelkarvraj21197@gmail.com

Viraj Karambelkar (Caltech), Tomas Ahumada (Caltech), Sam Rose (Caltech), Kaew Tinyanont (NARIT), Christoffer Fremling (Caltech), Nicholas Earley (Caltech), and Mansi Kasliwal (Caltech) report:

We observed the transient AT2025bbo (GCN 39210; 39244) with the Near-Infrared Echelle Spectrograph (NIRES, Wilson et al. 2004) on the Keck II telescope on 2025-02-10 05:29:43 UTC. Our observations comprised six exposures of 300s each. The spectra were extracted using the idl package spextool (Cushing et al. 2003, Vacca et al. 2004)

The spectrum shows several absorption features attributable to the host galaxy (CN, Mg I, Si I, CO absorption) at a redshift of z=0.070+/-0.001, consistent with the redshift reported in GCN 39272. No obvious features attributable to a supernova or AGN are visible. Further analysis is in progress.

We thank the Keck Observatory staff (Carlos Alvarez and Rita) and the Keck II observers (Maissa Salama and Becky Jensen-Clem) for their cooperation with the Target of Opportunity observations.

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