TITLE:   GCN CIRCULAR
NUMBER:  37228
SUBJECT: EP240801a: Keck/LRIS spectroscopic redshift confirmation
DATE:    24/08/22 08:10:26 GMT
FROM:    Weikang Zheng at UC Berkeley <weikang@berkeley.edu>

WeiKang Zheng, Thomas G. Brink, Alexei V. Filippenko (UCB),

Rebecca Davies and Adam Deller (Swinburne),

report on behalf of the KAIT GRB team:


Following the detection of EP240801a (Zhou et al., GCN 36997),

we observed its GRB optical counterpart (Fu et al., GCN 36998;

Li et al., GCN 36999; Zheng et al., GCN 37000; Aryan et al.,

GCN 37002; An et al., GCN 37004; Pérez-Fournon et al., GCN

37007; Malesani et al., GCN 37008; Zhu et al., GCN 37010;

Moskvitin & Spiridonova, GCN 37012; Quirola-Vásquez et al.,

GCN 37013; Moretti et al., GCN 37014; Turpin et al., GCN 37015;

Pankov et al., GCN 37016; Moskvitin & Spiridonova, GCN 37017;

Ruocco et al., GCN 37024; Pankov et al., GCN 37040; Moskvitin

et al., GCN 37049; Pankov et al., GCN 37146) with the Low

Resolution Imaging Spectrometer (LRIS, Oke et al. 1995) at the

Keck I Observatory (ToO program U232, PI A. V. Filippenko).

Observations started at 2024-08-02 09:36 (~1.02 days after the

burst), and consisted of 3 x 950 s exposures with the 600/4000

grism and 400/8500 grating. The spectrum shows a well-detected

continuum. We detect narrow absorption lines consistent with

Mg II 2796, 2803 Ang doublet as well as Fe II 2600 Ang,

confirming the redshift of z = 1.673 reported by Quirola-Vásquez

et al. (GCN 37013) from GTC.


We thank Josh Walawender and Matthew Wahl from the Keck team for

their support during this Target of Opportunity trigger. The data

presented herein were obtained at the W. M. Keck Observatory,

which is operated as a scientific partnership among the California

Institute of Technology, the University of California, and the

National Aeronautics and Space Administration. The Observatory was

made possible by the generous financial support of the W. M. Keck

Foundation. The authors wish to recognize and acknowledge the very

significant cultural role and reverence that the summit of Maunakea

has always had within the indigenous Hawaiian community. We are

most fortunate to have the opportunity to conduct observations from

this mountain.