[vsnet-grb-info 14765] GRB 111225A: Archeological redshift of the Christmas Burst 2011 from GTC

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16079
SUBJECT: GRB 111225A: Archeological redshift of the Christmas Burst 2011 from GTC
DATE:    14/04/04 11:37:47 GMT
FROM:    Christina Thoene at IAA-CSIC  <christina.thoene at gmail.com>

C.C. Thoene (IAA-CSIC) and A. de Ugarte Postigo (IAA-CSIC, DARK/NBI)
report on behalf of a larger collaboration:

We observed the Christmas burst of 2011, GRB 111225A (Siegel et al. GCN
12720), with the 10.4m GTC telescope+OSIRIS on December 25, 2011 at a mean
time 23:27 UT, 19.61 hrs after the burst. The observations consisted of
2x1800 s exposure with grism R1000B, covering the wavelength range from
3700 to 7870A with a resolution of around R=1000.

Initial analysis of the spectrum revealed continuum emission over the
complete range but no significant features neither in absorption nor
emission. However, a more careful analysis recently performed on the data
with an improved pipeline revealed faint emission features of [OII], H-beta
and [OIII], and marginal absorption of CaII at a common redshift of
z=0.297, which we therefore identify as the redshift of the GRB.

We apologise for the late notification. Better late than never.