TITLE: GCN CIRCULAR NUMBER: 38126 SUBJECT: EP241107a: Gemini-South spectroscopic confirmation (z = 0.456) DATE: 24/11/08 08:46:39 GMT FROM: Jonathan Quirola at Radboud University jaquirola1990@gmail.com

J. Quirola-Vasquez (Radboud Univ.), F.E. Bauer (PUC), P.G. Jonker (Radboud Univ.), D.B. Malesani (DAWN/NBI & Radboud Univ.), A.J. Levan (Radboud), report for a larger collaboration:

We observed the optical counterpart of EP241107a (Odeh et al., GCN 3 8115; Kang et al., GCN 38116; Lipunov et al., GCN 38117; Mohan et al., GCN 38118; Busmann et al., GCN 38120) detected by EP-WXT (Zhou et al., GCN 38112) using the Gemini-South (GS) telescope equipped with the Gemini Multi-Object Spectrograph (GMOS) instrument, and the grating R400.

We started observing the target on 2024-11-08 03:05:08.6 UT (i.e., ~12.9 hr after the X-ray trigger), taking four spectra (4x800 s) and covering the wavelength range ~5000-9500 AA. A continuum is clearly detected, as well as several emission lines, which we interpret as [O III] 4959,5007, Hbeta, and a marginal detection of [O II] 3727, also mentioned by Adami et al. (GCN 38122), all at a common redshift z = 0.456. This value is broadly consistent with the one reported by Adami et al. (GCN 38122) and the photometric redshift of the host galaxy reported in the Legacy catalog z= 0.523+-0.106 (Zhou et al. 2021).

We acknowledge expert support from the Gemini South staff.

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