GCN Circular 45675
Subject
EP260920b: VLT/X-shooter spectroscopic redshift z = 3.582
Event
Date
2026-09-21T09:47:13Z (10 days ago)
From
Valerio D'Elia at ASDC <valerio.delia@ssdc.asi.it>
Via
Web form
B. Schneider (LAM), A. Saccardi (CEA/Irfu), J. An (NAOC), D. Xu (NAOC), V. D’Elia (ASI/SSDC), M. Garnichey (LUX-Paris Obs.), G. Corcoran (UCD), N. R. Tanvir (U. Leicester), report on behalf of the Stargate collaboration:
We observed the optical counterpart (Liu et al., GCN 45668; García-García et al., GCN 45669; Li et al., GCN 45671; Eyles-Ferris et al., GCN 45673) of the EP260920b (Ni et al., GCN 45664; Yang et al., GCN 45670) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.
The acquisition images, which started at 03:51:03 UT of 21 Sep 2026 (13h44m after the EP trigger) show the counterpart with the following photometry (AB magnitudes), calibrated against Pan-STARRS and not corrected for Galactic extinction:
g = 22.6 +/- 0.1
r = 21.6 +/- 0.1
z = 21.3 +/- 0.2
A spectrum covering the wavelength range 3000-21000 AA was secured, with a total exposure time of 4x600 s in each of the UVB, VIS, and NIR arms. Our observation started at 04:00:42 UT on 2026 September 21, i.e. about 13h53m after the EP trigger.
We detect afterglow continuum in each arm. We can see Si II, C IV, Al III, Fe II, and likely Mg II, C II and C II*, the Lyman-alpha absorption trough (near the edge of the VIS arm), and the Lyman forest with Lyman-beta, -gamma, -delta, and Lyman-limit features at slightly lower S/N, all under a common redshift of z = 3.582. Based on this, we infer that this is the redshift of EP260920b.
We also detect an intervening system at z = 1.625.
We acknowledge excellent support from the ESO staff in Paranal.