TITLE: GCN CIRCULAR NUMBER: 41160 SUBJECT: GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26 DATE: 25/07/25 10:24:26 GMT FROM: Nusrin Habeeb at University of Leicester <nh312@leicester.ac.uk> A. L. Thakur (INAF-IAPS), N. R. Tanvir (Univ. of Leicester), A. de Ugarte Postigo (LAM), A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACn and DARK/NBI), A. Kumar (RHUL), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration: We observed the optical counterpart (Buckley et al. GCN 41151; Li et al. GCN 41158; Perez-Garcia et al. GCN 41159) of GRB 250725A (Fermi GBM Team, GCN 41150; Evans et al. GCN 41152) using the ESO/VLT UT1 (Antu) equipped with the FORS2 spectrograph. In a 60 s acquisition image obtained in I-band starting on 2025 July 25 at 07:44:31 UT (5.88 hrs after the burst), the afterglow is well detected with I(AB) = 20.5+/-0.1 mag, calibrated against nearby stars from the SkyMapper catalog. We obtained a single exposure of 1800 s using grism 300I+11 starting on 2025 July 25 at 08:04:47 UT (6.22 hrs after the burst). In a preliminary reduction of the spectrum, a trough due to Lyman-alpha is visible at 7610AA. From the detection of metals absorption features, which we interpret as due to O I and Si II, plus a tentative Si II* fine structure line, we infer a redshift of z = 5.26. At that same redshift we also detect an absorption feature consistent with Lyman-beta from the host galaxy, within the Lyman forest. We acknowledge the excellent support from the ESO observing staff in Paranal, in particular Carlos La Fuente and Lorena Faundez. View this GCN Circular online at https://gcn.nasa.gov/circulars/41160. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...