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GCN Circular 35936

X-ray transient EP240315a: VLT/X-shooter spectroscopic redshift of z = 4.859
2024-03-17T06:54:26Z (2 months ago)
Andrea Saccardi at Observatoire de Paris <>
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A. Saccardi (GEPI/Obs. de Paris), A. J. Levan (Radboud Univ. & Warwick Univ.), Z. Zhu (NAOC), B. P. Gompertz (U. Birmingham), S. D. Vergani (GEPI/Obs. de Paris & IAP & INAF/OABr), G. Pugliese (API), D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), report on behalf of the Stargate collaboration:

We observed the field of the ATLAS optical counterpart AT2024eju (Srivastav et al., GCN 35932) of the fast X-ray transient EP240315a reported by the WXT instrument during the commissioning phase of the Einstein Probe mission (Zhang et al, GCN 35931) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 1200 s each. Observations started at 01:02:52 UT on Mar 17 2024 (~29 hr after the trigger). We detect a clear continuum across both VIS and NIR arms. From the detection of a Lya absorption at ~7120 AA and multiple absorption features, which we interpret as being due to OI, SiII, NV, CIV and SiIV, we infer a redshift of z = 4.859. We also note the presence of additional absorption features likely due to multiple intervening systems. The high redshift of the transient suggests a highly energetic event and potentially links this Fast X-ray Transient to a GRB-like phenomena.

We acknowledge the excellent support from the ESO staff in Paranal, in particular Joe Anderson and Matias Jones.
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