[vsnet-grb-info 16906] GRB 150821A: VLT/X-shooter redshift
GCN Circulars
gcncirc at capella2.gsfc.nasa.gov
Fri Aug 21 20:30:12 JST 2015
TITLE: GCN CIRCULAR
NUMBER: 18187
SUBJECT: GRB 150821A: VLT/X-shooter redshift
DATE: 15/08/21 11:30:04 GMT
FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani at dark-cosmology.dk>
V. D'Elia (ASI/ASDC and INAF-OAR), T. Kruehler (ESO), K. Wiersema (U.
Leicester), N. R. Tanvir (U. Leicester), J. Japelj (U. Ljubljana), G.
Pugliese (API/UvA), D. Malesani (DARK/NBI), B. Milvang-Jensen
(DARK/NBI), J. P. U. Fynbo (DARK/NBI), report on behalf of a larger
collaboration:
We observed the optical counterpart of GRB 150821A (Troja et al., GCN
18186) with the ESO VLT equipped with the X-shooter spectrograph. Four
spectra with individual exposure time of 600 s were secured covering the
wavelength range 3,000-25,000 AA. Observations were carried out in
robotic "rapid response mode" (RRM) and spectroscopy began 12.4 min
after the BAT trigger (7.7 min after the XRT position, at which point
the VLT was triggered). The afterglow is well detected in our
acquisition image, with a magnitude of R ~ 16 (11.1 min after the GRB),
calibrated to one nearby USNO star.
We detect a number of absorption features at a common redshift of z =
0.755, including Mg II, Mg I, Fe II, Zn II. We also detect
fine-structure lines at the same redshift (e.g. FeII* 2396 / 2389, and
Ni II** 2166 / 2217 / 2223), confirming that the absorption system is
local to the GRB and not intervening.
We thank the kind assistence of the observing staff at Paranal, in
particular Claudia Cid and Marcela Espinoza.
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