GCN Circular 40901
Subject
GRB 250702F: GTC/OSIRIS+ spectroscopic redshift z = 1.520
Event
Date
2025-07-02T23:48:29Z (a day ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), G. Lombardi (GTC), J. F. Agui Fernandez (CAHA), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), S. Geier (GTC), L. Izzo (INAF/OACN and DARK/NBI), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), C. C. Thoene (AbAO), F. Pérez (GTC), D. l. Pérez Valladares (GTC) and A. Tejero Caro (GTC) report:
We observed the optical afterglow of GRB 250702F detected by Swift (Klingler et al., GCN 40894) and Fermi (Fermi GBM team, GCN 40892), using the 10.4 m GTC located at the Roque de los Muchachos Observatory in the island of La Palma (Spain) equipped with the OSIRIS+ instrument.
Our spectroscopic observations started on 2025-07-02 at 22:36:29 UT (1.496 hr after the Swift trigger) and consisted of 2x420 s exposures using grism R1000B, which covers the wavelength range between 3600 and 7700 AA.
On top of the bright continuum, a number of clear absorption features are detected. Among many, we identify C IV, Al II, Al III, Fe II, Mg II, Mg I, all at a common redshift z = 1.520. This is likely the redshift of GRB 250702F.