TITLE: GCN CIRCULAR NUMBER: 42994 SUBJECT: GRB 251201B: SALT spectroscopic redshift z = 1.599 DATE: 25/12/04 23:55:00 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute daniele.malesani@nbi.ku.dk
D. B. Malesani (DAWN/NBI and Radboud), A. J. Levan (Radboud and Warwick), S. de Wet (DTU Space), A. de Ugarte Postigo (LAM), D. A. H. Buckley (SAAO), A. Martin-Carrillo (UCD), P. M. Vreeswijk (Radboud) report on behalf of a larger collaboration:
We observed the optical afterglow of the Swift and Fermi GRB 251201B (Moss et al., GCN 42924; Palafox & Meegan, GCN 42965), using the Robert Stobie Spectrograph (RSS) installed on the 9.2 m Southern African Large Telescope (SALT) at the Sutherland observatory (South Africa).
In a 10-s acquisition image, taken with the SALTICAM instrument on 2025 Dec 1.871 UT (4.47 hr after trigger), we measure a magnitude i = 19.25 +- 0.09 AB, calibrated against nearby stars from the Pan-STARRS catalog, and not corrected for Galactic extinction.
A 2400-s spectrum was acquired using the PG0700 grating, covering the wavelength range 3600-7500 AA. Faint continuum is detected across the entire spectrum, setting a secure upper limit to the redshift z < 2. Towards the red end, we identify a few weak absorption features, which we match to Mg I 2852, Mg II 2804, 2796, Fe II 2600, 2587, 2383, all at a common redshift of z = 1.599, which we suggest to be the redshift of GRB 251201B.
We acknowledge excellent support from the SALT observing staff, in particular Alexei Kniazev and Veronica Van Dyk.
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