TITLE:   GCN CIRCULAR
NUMBER:  37122
SUBJECT: GRB 240809A: Tentative redshift from NOT
DATE:    24/08/09 23:39:17 GMT
FROM:    Antonio de Ugarte Postigo at OCA <deugarte@oca.eu>

Rashmi Gottumukkala (DAWN/NBI), Chandana Chandrasherkhar Hegde (DAWN/DTU), Jens Reersted Larsen (IFA), Ulrika Woulhoj Jakobsen (DTU), Rasmus Damgaard Nielsen (DAWN/NBI), Nikolaj Bjerregaard Sillassen (DAWN/DTU), Albert Bjerregard Sneppen (DAWN/NBI), Johan P. U. Fynbo (DAWN/NBI), Antonio de Ugarte Postigo (CNRS), Daniele B. Malesani (DAWN/NBI and Radboud Univ.) and Nial R. Tanvir (U. Leicester) report:

We observed the afterglow of GRB 240809A (Evans et al. GCN 37110; Want et al. GCN37113; Dubai et al. GCN37114; Jiang et al. GCN 37116) with ALFOSC on the 2.5 m Nordic Optical Telescope (La Palma, Spain). The observation consisted of 300 s imaging in r-band followed by 4x1200 s spectroscopy covering the range between 3500 and 9500 AA. The observation started at 2024 Aug 9.87846 UT, 12.575 hr after the burst. 

The afterglow is well detected in imaging at r ~ 20.3 mag. The spectrum shows continuum emission over the complete spectral range. We identify marginal spectral features which seem to match Mg II, Mg I and Fe II at a common redshift of 1.495, which we propose as the most likely redshift of this GRB.

Further observations to confirm this measurement are encouraged.