TITLE: GCN CIRCULAR NUMBER: 31480 SUBJECT: GRB 220117A: VLT/X-shooter optical afterglow and redshift DATE: 22/01/18 12:25:23 GMT FROM: Daniele B Malesani at Radboud U J. Palmerio (CNRS, GEPI - Paris Observatory), D. B. Malesani (Radboud Univ. and DAWN/NBI), J. P. U. Fynbo (DAWN/NBI), D. Xu (NAOC), L. Izzo (DARK/NBI), S. Y. Fu (NAOC), Z. P. Zhu (NAOC, HUST), D. A. Kann (IAA/CSIC), N. R. Tanvir (Univ. Leicester) report on behalf of the Stargate collaboration: We observed the field of GRB 220117A (Melandri et al., GCN 31466) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our first observations were carried out using the acquisition camera, using the g, r and z filters (3x60 s in each band). Inside the XRT error circle (Beardmore et al., GCN 31472), we detect a new source, not visible in the archival Pan-STARRS images, which we identify as the GRB afterglow. The source is very red, being detected strongly in z, only weakly in r, and completely missing in g. Calibrated against nearby stars from the Pan-STARRS catalog, we measure z = 20.81 +- 0.12 mag and z - r ~ 2.1 mag (all AB magnitudes). The afterglow coordinates are (J2000, 0.2" error): RA = 06:06:17.409 Dec = -28:26:15.78 A spectrum was secured covering the wavelength range 3000-21000 AA, and consisting of 4 exposures of 1200 s each. The observation mid time was 2022 Jan 18.15 UT (11.3 hr after the GRB). In a preliminary reduction, continuum is detected in the red part of the spectrum down to ~7260 AA. We interpret the break as due to Lyman alpha. The absorption system is rather weak and, at the present time, we identify with confidence only the Lyman-alpha trough and the Si II 1260 AA feature, which correspond to a redshift z = 4.961 for GRB 220117A. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Michael Abdul-Masih, Diego Parraguez, and Jonathan Smoker.