TITLE: GCN CIRCULAR NUMBER: 40265 SUBJECT: EP250427A/GRB250427A: Keck/LRIS redshift DATE: 25/04/27 14:11:22 GMT FROM: Ryan Chornock at UC Berkeley chornock@berkeley.edu
R.Chornock, E. Hammerstein, X. Guo (UC Berkeley) report:
We observed the optical afterglow (GCNs 40258, 40259, 40260, 40261, 40263, 40264) of EP250427a (GCN 40257)/GRB 250427a (GCN 40262) using the Low-Resolution Imaging Spectrometer on the Keck-I telescope at a mean time of 12:36UT on 2025 Apr 27. Observations covered the range 3140-10300 Angstroms.
A continuum is well detected across the full spectral range with many absorption lines present. We identify a strong doublet at observed wavelengths of 3900.3,3906.7 Angs as CIV at z=1.519 from the highest redshift system detected. There are also many lines (C II, C IV, Fe II, Mg I, Mg II) from a stronger low-redshift system at z=1.406.
Further analysis is ongoing.
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