[AAVSO-HEN] GRB 091516: VLT spectrum (correction & update)

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TITLE:   GCN CIRCULAR
NUMBER:  9383
SUBJECT: GRB 091516: VLT spectrum (correction & update)
DATE:    09/05/17 08:38:02 GMT
FROM:    Antonio Deugarte at IAA-CSIC  <deugarte at iaa.es>

A. de Ugarte Postigo (ESO), J. Gorosabel (IAA/CSIC), D. Malesani,
J.P.U. Fynbo (DARK/NBI), A. J. Levan (Univ. Warwick), report on
behalf of a larger collaboration:

We have reanalysed the spectrum of the afterglow of GRB090416
(Rowlinson et al., GCN 9374; Guidorzi et al., GCN 9375) obtained
with the ESO VLT (de Ugarte Postigo et al. GCN 9381). Due to an
error in the preliminary reduction, the wavelength calibration had an
offset that has been now corrected.

In our new analysis we detect a strong Ly-alpha absorption
together with absorption lines of NV, SII, SiII, NiII, CI, SiIV, CIV,
FeII, AlII, AlIII as well as SiII* at a redshift of 4.109+/-0.002,
which we identify as the redshift of the afterglow. This is in
agreement with the photometric redshift obtained with GROND (Rossi
et al. GCN 9382).

The spectrum also shows an intervening system at z=2.697+/-0.002,
characterised by the presence of several FeII absorption lines.