GCN Circular 38004
Subject
GRB 241030B: GTC/OSIRIS+ tentative spectroscopic redshift z = 2.82
Event
Date
2024-10-31T11:54:00Z (a year ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
N. R. Tanvir (U. Leicester), C. C. Thoene (ASU-CAS, AbAO), J. P. U. Fynbo (DAWN/NBI), A. de Ugarte Postigo (LAM/OCA, CNRS), L. Izzo (INAF-OACn & DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), J. F. Agui Fernandez (CAHA), G. Lombardi (GTC), S. Geier (GTC) and G. Gómez Velarde (GTC) report:
We observed the optical counterpart (Fu et al., GCN 37985) of GRB 241030B (Fermi GBM team, GCN 37980; Klingler et al., GCN 37981; Zhao et al., GCN 37984) using OSIRIS+ on the 10.4 m GTC telescope, at the Roque de los Muchachos Observatory (La Palma, Spain). The observation consisted of 4 spectra of 1200 s each, obtained with grism R1000B, covering the spectral range between 3650 and 7800 AA, at a resolving power of 600.
The acquisition image, obtained on 2024-10-31 at 02:42:33 UT, 8.14 hr since the trigger, shows the afterglow at r(AB) = 23.53 +/- 0.12 mag, as compared to Pan-STARRS field stars.
The spectrum shows a faint continuum over the complete spectral range, though a drop in flux is observed blueward of ~4700 AA, suggesting the onset of the Lyman-alpha forest. No clear DLA trough is visible, but several, low S/N absorption features are present to the red of the drop, which we tentatively interpret as Si II 1526, Si IV 1393, C IV 1548,1550 (blended), Al II 1670, Al III 1854,1862 at z = 2.82, which we propose as the redshift of GRB 241030B.