TITLE:   GCN CIRCULAR
NUMBER:  37677
SUBJECT: GRB 241001A: VLT/X-shooter redshift
DATE:    24/10/02 12:20:51 GMT
FROM:    J. T. Palmerio at Observatoire de Paris - GEPI <jesse.palmerio@obspm.fr>

J. T. Palmerio (CEA), B. Schneider (MIT), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Saccardi (GEPI/Obs. de Paris), L. Izzo (INAF-OACn & DARK/NBI), P. D’Avanzo (INAF-OAB), S. D. Vergani (GEPI/Obs. de Paris), A. de Ugarte Postigo (LAM/OCA, CNRS) and  A. J. Levan (Radboud Univ.)  report on behalf of the Stargate collaboration:

We observed the optical counterpart of the SVOM/ECLAIRs GRB 241001A (Schanne et al., GCN 37655) 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. The observations mid-time is 07:11:17 UT on 2024 October 02 (~14 hours after the SVOM timeTb).


In a 60 s image taken with the acquisition camera, we detect the optical afterglow (Izzo & Malesani, GCN 37673), for which we measure an AB magnitude r = 22.3 (calibrated against nearby stars from the Legacy Survey DR10 catalog).


In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. From the detection of multiple absorption features, which we interpret as due to Fe II and Mg II, we infer a common redshift of z = 0.5727. We also detect bright emission lines ([O II] and [O III] doublets, and Hbeta) at a consistent redshift of z = 0.5730, which we interpret as being due to the GRB host galaxy. We conclude that GRB 241001A is at z = 0.573.


We acknowledge expert support from the ESO staff in Paranal, in particular Diego Parraguez and Michael Marsset.