TITLE: GCN CIRCULAR NUMBER: 37013 SUBJECT: EP240801a: GTC spectroscopy and absorption redshift DATE: 24/08/02 10:44:40 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl> J. Quirola-Vásquez (Radboud Univ.), J. van Dalen (Radboud Univ.), D. B. Malesani (DAWN/NBI and Radboud Univ.), P. G. Jonker (Radboud Univ), A. J. Levan (Radboud Univ. & Warwick Univ.), F. E. Bauer (PUC), M. E. Ravasio (Radboud Univ.), D. Mata Sanchez (IAC), M. A. P. Torres (IAC), report on behalf of a larger collaboration: We observed the optical counterpart of EP240801a (Zhou et al., GCN 36997; Fu et al., GCN 36998) using the 10.4 m GTC located in La Palma, Canary Islands. Observations started on 2024 Aug 2.169 UT (0.79 days after the EP trigger), consisted of 4 exposures of 1200 s each, and were carried out using grism R1000R, which covers the wavelength range 5100-10000 AA. The counterpart magnitude was r = 21.98 +- 0.05 (AB) as measured in a 30-s acquisition image, calibrated against nearby Pan-STARRS sources. Continuum is well detected over the entire wavelength range. Several absorption lines are visible, which we interpret as due to Mg II and Fe II at a common redshift z = 1.673, which we suggest to be the likely redshift of EP240801a. We acknowledge excellent support from the GTC staff, in particular Stefan Geier and Antonio Luis Cabrera Lavers. View this GCN Circular online at https://gcn.nasa.gov/circulars/37013. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...