[vsnet-grb-info 12264] GRB 120815A: VLT/X-shooter redshift

GCN Circulars gcncirc at capella2.gsfc.nasa.gov
Wed Aug 15 14:40:19 JST 2012


TITLE:   GCN CIRCULAR
NUMBER:  13649
SUBJECT: GRB 120815A: VLT/X-shooter redshift
DATE:    12/08/15 05:40:11 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

D. Malesani (DARK/NBI), S. Schulze (PUC and MCSS), A. de Ugarte Postigo 
(IAA/CSIC and DARK/NBI), D. Xu (WIS), V. D'Elia (INAF/Roma and 
ASI/ASDC), J. P. U. Fynbo (DARK/NBI), N. R. Tanvir (Univ. Leicester), 
report on behalf of a larger collaboration:

We observed the field of GRB 120815A (Pagani et al., GCN 13645) with the 
VLT/X-shooter spectrograph. We confirm the presence of a bright, 
uncatalogued object consisent with the GROND position (Sudilovsky et 
al., GCN 13648). From the acquisition images, we measure R = 18.9 for 
the afterglow at an epoch of 1.67 hr after the GRB (calibrated to nearby 
USNO stars).

Our spectra cover the wavelength range 3000-25000 AA, and were taken 
starting on 2012 Aug 15.163 UT (1.69 hr after the GRB), for a total of 
40 min exposure. Continuum from the afterglow is detected with high S/N 
in all of the UVB, VIS, and NIR arms.

The spectrum shows a wide trough and a multitude of strong absorption 
lines, which we interpret as due to a DLA and metal transitions of N V, 
S II, Si II, O I, C IV, Si IV, Fe II, Al II, Al III, Mn II, Mg II, Mg I, 
among others, at a common redshift z = 2.358. At the same redshift, we 
also detect fine-structure lines of Ni II and Fe II, thus confirming 
conclusively that this is the GRB redshift. We also detect intervening 
systems at z = 1.539, 1.693, and 2.00. In particular, the system at z = 
1.539 displays exceptionally strong Mg II, Mg I, and Fe II absorption.

We acknowledge the expert support of the VLT observing staff at Paranal, 
in particular Maja Vuckovic. We also thank Alex Kann for discussion on 
the afterglow identification.


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