GCN Circular 43932
Subject
EP260302a: Gemini-South redshift z = 1.535
Event
Date
2026-03-06T09:26:04Z (5 days ago)
Edited On
2026-03-06T22:15:19Z (4 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
A. J. Levan (Radboud), G. Corcoran (UCD), J. Quirola-Vasquez (Radboud), D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud), F. E. Bauer (UTa), J. Chácon (PUC), L. Cotter (UCD), R. A. J. Eyles-Ferris (Leicester), A. Martin-Carrillo (UCD), A. Cikota (NOIRLab), R. Ruiz (Gemini), V. Firpo (Gemini) report on behalf of a larger collaboration:
Taking advantage of its rebrightening (Corcoran et al., GCN 43928), we observed the optical counterpart (Li et al., GCN 43898; Pérez-García et al., GCN 43903; Corcoran et al., GCNs 43904, 43928) of the fast X-ray transient EP260302a (Zhang et al., GCNs 43899, 43906) using Gemini-South equipped with the GMOS spectrograph.
In the acquisition image (mid time 3.18 days after trigger) we measure r = 21.30 +- 0.07 AB, suggesting some fading compared with our previous observation (Corcoran et al., GCN 43928).
Four exposures of 600 s each were obtained, using grating B480, a slit width of 1 arcsec, and covering the wavelength range 4470-8500 Å. The observation mid time was 2026 March 6.182 UT (3.20 days after the EP/WXT trigger).
Continuum is significantly detected over the entire covered wavelength range. From the lack of Hydrogen absorption, we infer a firm upper limit z < 2.67. A number of clear absorption features are also visible, which we interpret as Fe II (2344, 2374, 2383, 2586, 2600 AA) and Mg II (2796, 2803 AA), all at a common redshift z = 1.535. Given the good S/N of the continuum, and the lack of any further unidentified features, we therefore conclude that EP260302a likely lies at this redshift.