GCN Circular 38097
Subject
GRB 241105A: VLT/FORS2 spectroscopic redshift z = 2.681
Date
2024-11-06T09:31:01Z (6 months ago)
Edited On
2024-11-11T16:05:39Z (6 months ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
L. Izzo (INAF-OACn & DARK/NBI), A. A. Chrimes (ESA/ESTEC & Radboud Univ.), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Saccardi (CEA/Irfu), A. Martin-Carrillo (UCD), A. J. Levan (Radboud Univ. and Warwick Univ.), B. P. Gompertz (Birmingham), N. R. Tanvir (U. Leicester), report on behalf of the Stargate collaboration:
We observed the proposed optical counterpart (Julakanti et al., GCN 38088) of GRB 241105A (Fermi GBM team, GCN 38085; DeLaunay et al., GCN 38091). We used the FORS2 spectrograph mounted on the ESO VLT UT1 (Antu), equipped with grisms 300V (without order-sorting filter) and 300I (with filter OG590). The exposure time was 600 s per grism. Spectroscopy started on 2024 November 6.133 UT (about 11.08 hr after the trigger), and was carried out through moderately good seeing conditions (1").
In the acquisition image, we measure a preliminary magnitude R = 20.10 +/- 0.10 (Vega), calibrated using archival FORS2 zeropoints.
From a preliminary reduction of the 300V spectrum, a continuum is detected over the wavelength range 4600 to 8700 AA. A trough due to Lya absorption is visible at the blue end. From the detection of multiple absorption features, which we interpret as due to C II, C IV, Si II, Si IV, Al II, Al III and Fe II, we infer a redshift of z = 2.681.
We acknowledge the excellent support from the ESO staff in Paranal, in particular Edouard Gonzalez, Maria Jose Rain, Luca Sbordone and Israel Blanchard.
Note: The redshift value originally reported was z=2.702. The refined value was obtained using updated calibration data (see Izzo et al., GCN 38167).