TITLE: GCN CIRCULAR NUMBER: 41639 SUBJECT: EP250827b: Gemini Spectroscopy of AT 2025wkm DATE: 25/09/01 20:27:47 GMT FROM: Anna Y Q Ho at Cornell University <ayh24@cornell.edu> Cassie Sevilla and Anna Ho (Cornell) report on behalf of the ZTF collaboration: We acquired long-slit spectroscopy of AT 2025wkm (possibly associated with Einstein Probe X-ray flare EP250827b; Schroeder et al. GCN #41635) using GMOS-N at Gemini Observatory on 2025-08-31 12:15:31 UTC, under the target-of-opportunity program GN-2025B-Q-130 (PI Ho). The observation was carried out with a 1" slit, the R400 grating, and the GG455 filter. We took four 450s exposures, two at a central wavelength of 710 nm and two at 720 nm. The data was reduced using DRAGONS. The spectrum shows a blue continuum with narrow emission lines of H alpha, H beta, [O III], and [S II] at a consistent redshift of z=0.120. The implied peak measured absolute magnitude of AT 2025wkm is M_g = -19.5 mag, corrected for Milky Way extinction. The rapid rise (~3d) to such a high luminosity is unusual for extragalactic transients. We thank the Gemini Observatory staff for assistance in rapidly obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41639. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...