GCN Circular 8191
Subject
GRB 080905B: VLT redshift
Event
Date
2008-09-07T00:16:14Z (18 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@astro.ku.dk>
Paul M. Vreeswijk, Johan P. U. Fynbo, Daniele Malesani, Jens Hjorth
(DARK/NBI), Antonio de Ugarte Postigo (ESO), report on behalf of a
larger collaboration:
We observed the field of GRB 080905B (Stroh et al., GCN 8182) with the
ESO VLT equipped with FORS2. Several spectra were obtained with
different grism choices, beginning on 2008 Sep 6.053 UT (8.34 hr after
the GRB), and covering the wavelength ranges 3800-9500 AA at low to
moderate resolution.
In the acquisition images, we clearly detect a point source inside the
refined XRT error circle (Osborne et al., GCN 8189), at the coordinates
(J2000):
RA = 20:06:57.90
Dec = -62:33:46.8
This position is consistent with that of the UVOT candidate afterglow
reported by Stroh et al. (GCN 8182), the object being now significantly
fainter (R ~ 20.2). We note that this position is 3.8" off the center of
the bright 2MASS galaxy 2MASX J20065732-6233465, also visible in the DSS
and in the UVOT images.
Spectroscopy of the afterglow reveals resonance absorption features from
several ions, including OI, SiII, CIV, FeII, AlII, AlIII, MgII, MgI, at
a redshift z = 2.374. The detection of transitions from fine-structure
levels of FeII indicates that this is the redshift of the GRB, under the
assumption that these levels are populated by GRB afterglow ultraviolet
photons. We also find evidence for an intervening absorber at z = 1.438.
We acknowledge excellent support from the Paranal staff, in particular
Elena Mason and Andres Pino.