J. T. Palmerio (GEPI / Paris Obs. and IAP), D. B. Malesani (Radboud Univ. and DAWN/NBI), A. Saccardi (GEPI / Paris Obs.), L. Izzo (INAF/OACn & DARK/NBI), P. Schady (Univ. Bath), A. de Ugarte Postigo (OCA) report on behalf of the STARGATE collaboration:
We observed the optical afterglow candidate of GRB 230628E (Malesani et al. GCN 34118) with the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.
Spectroscopy was carried out, covering the wavelength range 3000-21000 AA, and consisting of 4 exposures of 600 s each. The observation mid time was 2023 June 29 at 01:05 UT (~2.7 hours after the GRB).
Only a faint continuum is detected from this source down to ~3700 Angstrom, which allows us to set a redshift upper limit z <~ 2.
We note a possible, very faint emission feature at ~15550 Angstrom but in the absence of other associated emission features, we do not derive a redshift from this.
We acknowledge expert support from the observing staff in Paranal, in particular Eleonora Sani, Thomas Romain, Ditte Slumstrup, and Thomas Rivinius.