TITLE:   GCN CIRCULAR
NUMBER:  36296
SUBJECT: LIGO/Virgo/KAGRA S240422ed: Magellan Spectrum of GW-MMADS Candidate AT2024hdo Indicates a Type II SN
DATE:    24/04/25 00:59:38 GMT
FROM:    Ryan Foley at UC Santa Cruz <foley@ucsc.edu>

A. L. Piro, J. D. Simon (Carnegie), A. Polin (Carnegie/Purdue), D. A. Coulter (STScI), M. R. Drout (Toronto), R. J. Foley, and C. Rojas-Bravo (UC Santa Cruz)

report on behalf of the Carnegie Gravitational wave ElectroMagnetic follow-up (CGEM) and the One-Meter Two-Hemisphere (1M2H) collaborations:

As part of our ongoing search for optical counterparts to the candidate gravitational wave event S240422ed using the 6.5m Magellan Clay telescope with the LDSS-3 spectrograph, we have obtained an optical spectrum of the DECam-reported counterpart candidate AT2024hdo (GCN 36273).

We obtained 2x1200s spectra of AT2024hdo and its presumed host galaxy with the VPH-All grating spanning 4000-10000A. The host galaxy has strong emission lines at z = 0.0658.  Examination of the spectrum of AT2024hdo reveals broad P-Cygni H-alpha emission consistent with a Type II SN at z = 0.0658.  We therefore conclude that AT2024hdo is unlikely to be associated with S240422ed.

We thank Marcelo Mora, Povilas Palunas, and the rest of the LCO staff for making these observations possible.