[vsnet-grb-info 12494] GRB 121011A: NOT redshift retraction

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13862
SUBJECT: GRB 121011A: NOT redshift retraction
DATE:    12/10/12 09:20:33 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

J. P. U. Fynbo (DARK/NBI), D. Malesani (DARK/NBI), D. Xu (WIS), report 
on behalf of a larger collaboration:

We performed a careful analysis of the spectrum secured at the NOT 
(Fynbo et al., GCN 13856) of the afterglow of GRB 121011A (Racusin et 
al., GCN 13845). We confirm that a faint continuum is visible in our 
data, but we cannot detect any clear feature with confidence. The 
redshift z = 0.58 suggested in GCN 13856 is therefore not correct.

A sharp break is detected at the blue end of our spectrum around 4100 
AA, but its interpretation is not straightforward. If due to Ly alpha at 
z = 2.3, than we would expect surviving flux blueward of the break. If 
due to the Lyman limit at z = 3.4, than we would expect to see the Lyman 
forest redward of the break, which we do not. We thus believe this break 
to be an artifact of the data, but encourage other observers to attempt 
spectroscopy with large area telescopes, also given the detection of the 
GRB by Fermi/LAT (Ohno et al., GCN 13859).