GCN Circular 13862
Subject
GRB 121011A: NOT redshift retraction
Date
2012-10-12T09:20:33Z (12 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@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).