GCN Circular 43469
Subject
EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
Event
Date
2026-01-20T09:45:18Z (6 months ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
G. Corcoran (UCD), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), A. L. Cabrera Lavers (GTC), A. M. García Rodríguez (GTC) report on behalf of a larger collaboration:
We observed the optical counterpart (Fortin et al., GCN 43450; Eyles-Ferris et al., GCN 43452; Moskvitin & Spiridonova, GCN 43463; Liu et al., GCN 43464; Ma et al., GCN 43466; Zheng et al., GCN 43468) of the Einstein Probe fast X-ray transient EP260119a (Jiang et al., GCNs 43447, 43465) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ spectrograph. Our observations consisted of 4 exposures of 1200 s each, using grism R1000R and covering the wavelength range 5200-10200 Å. The observation mid time was Jan 20.156 UT (27.5 hr after trigger).
In the acquisition image, the target is detected with an AB magnitude z = 21.06 +- 0.10 (mid time 26.8 hr after trigger), calibrated against nearby Pan-STARRS objects and not corrected for Galactic extinction.
A trace is well detected in the red part of our spectrum, with a sharp break around 7870 Å. We interpret this as the onset of the Lyman forest at z ~ 5.47. The sharpness of the break indicates a low HI column density. No clear metal lines are identified in the currently available (preliminary) reduction of the spectra. Our spectroscopic measurement of the redshift is in broad agreement with, and refines, the photometric determination reported by COLIBRÍ (Fortin et al., GCN 43455).