{
  "format": "text/plain",
  "eventId": "GRB 250706B",
  "createdOn": 1751976296831,
  "bibcode": "2025GCN.41022....1P",
  "submitter": "Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>",
  "body": "J. T. Palmerio (CEA/Irfu), B. Schneider (LAM), A. Saccardi (CEA/Irfu), M. Garnichey (LUX-Paris Obs.), G. Corcoran (UCD), V. D'Elia (ASI/SSDC), M. De Pasquale (Univ. Messina), L. Izzo (INAF/OACn and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), P. O'Brien (Leicester), N. R. Tanvir (Univ. Leicester), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration:\n\nWe observed the optical afterglow (Zhu et al., GCN 40991) of the SVOM GRB 250706B (Palmerio et al., GCN 40989), an extension of GRB 250706C detected by Konus-Wind and Fermi/LAT (Frederiks et al., GCN 41013; Longo et al., GCN 41019), using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 2 exposures of 600 s each. The observation mid time was 2025 Jul 8.40 UT (1.70 days after the Konus-Wind trigger).\n\nIn a 30 s image taken with the acquisition camera on Jul 8.39 UT (1.69 days after the Konus-Wind trigger), the optical afterglow is clearly detected, and we measure a magnitude r = 20.37 +- 0.02 AB (calibrated against a single star from the SkyMapper catalog).\n\nIn a preliminary reduction of the spectra, continuum is visible over the entire covered wavelength range. From the detection a multitude of absorption lines, which we interpret as due to Al II, Ni II, Si II, Si II*, Al III, Cr II, Zn II, Ni II*, Fe II, Fe I, Mn II, Mg II, Mg I, Ca II, Ca I, we infer a redshift of z = 0.942. We also detect two emission lines which we identify as the [O III] 4959,5007 doublet at the same redshift. The detection of fine-structure lines, as well as of nebular emission, allows us to securely identify z = 0.942 as the redshift of GRB 250706B/C.\n\nWe acknowledge excellent support from the ESO observing staff in Paranal, in particular Diego Parraguez. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).",
  "circularId": 41022,
  "submittedHow": "web",
  "subject": "GRB 250706B/C: VLT/X-shooter redshift z = 0.942"
}