GCN Circular 31480

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
Not found
 
 
) 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
Not found
 
 
), 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.