A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), D.A. Kann (IAA-CSIC),
C.C. Thoene (IAA-CSIC), L. Izzo (IAA-CSIC), N.R. Tanvir (U. Leicester),
G. Lombardi (GTC, IAC), and A. Marante (GTC) report on behalf of a
We observed the field of GRB 170405A (Troja et al., GCN 20984; Hui
& Meegan, GCN 20986; Vianello & Kocevski, GCN 20987) using OSIRIS
on the 10.4m GTC at the Roque de los Muchachos observatory (La Palma,
Spain). The observation consisted of 3x900s using the R1000B grism,
covering the range between 3700 and 7800 ��. The first spectrum started at
2:14 UT (7.57 hr after the burst).
On a preliminary reduction based on archival calibrations we detect a
spectral continuum with strong absorption features, which we identify as
due to Ly-alpha, SiII, OI, CII, SiIV, CIV, FeII and AlII at a common redshift of
z = 3.510, which we identify as the redshift of the GRB.