[vsnet-grb-info 19295] GRB 170405A: Redshift from OSIRIS/GTC

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20990
SUBJECT: GRB 170405A: Redshift from OSIRIS/GTC 
DATE:    17/04/06 03:10:20 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte at iaa.es>

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 
larger collaboration:

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 Å. 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.