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GCN Circular 15470

Subject
GRB 131108A: Redshift from 10.4m GTC
Date
2013-11-09T05:35:00Z (10 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), C.C. Thoene (IAA-CSIC),
J. Gorosabel (IAA-CSIC), R. Sanchez-Ramirez (IAA-CSIC), 
J.P.U. Fynbo (DARK/NBI), N.R. Tanvir (U. Leicester), 
A. Cabrera-Lavers (ULL/IAC) and A. Garcia (ULL/IAC) report on 
behalf of a larger collaboration:

We have observed the afterglow of the Fermi-LAT GRB 131108A (Racusin 
et al. GCN 15464, Hurley et al. GCN 15466, Stroh et al. GCN 15468, Gorosabel 
et al. GCN 15469) with the 10.4m GTC telescope at Roque de los Muchachos 
Observatory (La Palma, Spain) starting at 04:50 UT (8.13 hr after the burst). 
The observation consisted of 3x600 s and was performed with the R1000B 
grism, that covers the range from 3700 to 7500 A at a resolution of ~1000.

Observations were performed with a poor seeing of ~2.2". The afterglow is 
detected in the acquisition frame with at a magnitude of r=18.9, as compared 
with the SDSS.

A preliminary reduction of the spectrum shows a strong trace and is 
characterised by a strong Ly-alpha absorption as well as absorption features 
which include SII, SiII, SiII*, OI, CII, SiIV, CIV and AlII at a common redshift of 
z=2.40, which we identify as the redshift of the GRB.
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