GCN Circular 43227
Subject
EP251222a: VLT/FORS2 spectroscopic redshift z = 0.505
Event
Date
2025-12-24T09:47:04Z (9 months ago)
From
Laura Cotter at University College Dublin <laura.cotter@ucdconnect.ie>
Via
Web form
J. An (NAOC), L. Izzo (INAF/OACn & DARK/NBI), A. Saccardi (CEA/Irfu), L. Cotter (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. L. Thakur (INAF-IAPS), D. Xu (NAOC), report on behalf of the Stargate collaboration:
We observed the optical counterpart (Li et al., GCN 43205; Malesani et al., GCN 43211) of EP251222a (Huang et al., GCN 43200; Guo et al., GCN 43216) with the ESO VLT UT1 (Antu) equipped with the FORS2 spectrograph. Our observations began on 2025 December 24 at 02:21:56 UT, 1.46 days post trigger.
A spectrum covering the wavelength range 3600-8600 AA was secured using grism 300V (with no order-sorting filter), with a total exposure time of 4x600 s.
In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. From the detection of multiple absorption lines, which we interpret as the Mg II doublet (2796, 2804) and Fe II (2587, 2600), we infer a redshift of z = 0.505. At a consistent redshift, we also detect emission lines due to the [O II] 3726,3729 doublet and [O III] 5007 from the host galaxy.
We acknowledge expert support from the observing staff in Paranal, in particular Elyar Sedaghati.