GCN Circular 40860
Subject
GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
Event
Date
2025-06-28T14:57:40Z (3 days ago)
From
J. An <jiean0813@foxmail.com>
Via
Web form
J. An (NAOC), B. Schneider (LAM), L. Izzo (INAF/OAC), R. Brivio (INAF/OABr), G. Corcoran (UCD), A. de Ugarte Postigo (LAM), B. P. Gompertz (Birmingham), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), report on behalf of a larger collaboration:
We observed the optical afterglow of GRB 250625A detected by Fermi/GBM (Godwin et al., GCN 40833) and Swift/BAT (Ferro et al., GCN 40825) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 1200 s each. The observation mid time was 2025 Jun 27.128 UT (34.98 hr after the GRB).
The slit was aligned to cover the optical afterglow (Moskvitin et al., GCN 40828; Xin et al., GCN 40830; Zhu et al., GCN 40834; Fortin et al., GCN 40837; Adami et al., GCN 40838; Brosio et al., GCN 40839; de Ugarte Postigo et al., GCN 40486). In a preliminary reduction of the spectra, we detect no obvious continuum nor any emission lines across the entire covered wavelength range. This could simply indicate that the emission lines of the actual (faint) GRB host galaxy are below our detection sensitivity, or, alternatively, would be consistent with an association with the nearby galaxy at z = 0.655 reported by de Ugarte Postigo et al. (GCN 40486).
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Célia Desgrange, Rodrigo Palominos, and Boris Häußler. We also thank Liping Xin (NAOC) and the SVOM/VT team for sharing accurate coordinates of the afterglow (see also GCN 40830).