[vsnet-grb-info 9007] GRB 100316B: VLT/X-shooter redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10495
SUBJECT: GRB 100316B: VLT/X-shooter redshift
DATE:    10/03/16 11:04:59 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo at brera.inaf.it>

S.D. Vergani (APC/Univ. Paris 7), P. D'Avanzo (INAF-OAB), D. Malesani, 
J.P.U. Fynbo, J. Hjorth (DARK/NBI), A.J. Levan (Univ. Warwick), H. Flores
(Paris Obs.), N.R. Tanvir (Univ. Leicester), P. Goldoni (APC/Univ. Paris 7
and SAp/CEA), L.A. Antonelli (INAF-OAR) report on behalf of a larger
collaboration:

We observed the optical afterglow of GRB 100316B (Baumgartner et al., GCN
10489; Afonso et al. GCN 10493; Haislip et al., GCN 10494) with the VLT
equipped with the X-shooter spectrograph. Observations started on 2010 Mar
16 at 08:43 UT (~ 40 minutes after the GRB), for a total exposure time of
4x600 s. From the acquisition image, we estimate for the optical afterglow
a magnitude of R = 18.2 +- 0.1 (calibrated against USNO-B1.0).
In a preliminary analysis of the specta, we clearly detect the continuum
in the UVB, VIS, and NIR arms, corresponding to the wavelength range
3200-24000 AA. We detect several absorption features, among these
FeII(1608), AlII(1670), AlIII(1854), FeII(2344), FeII(2374), FeII(2382),
MgII(2796, 2803) and MgI(2852) at a common redshift of z=1.180. The lack
of Lyman forest lines down to ~3200 AA sets an upper limit to the redshift
z<1.6. We also find evidence for FeII lines and MgII doublet from a strong
intervening systems at z=1.063.

We caution that the above analysis (particularly the wavelength solution)
is preliminary. Reduction with updated calibrations is underway. We would
like to thank the ESO staff for their kind assistance, in particular Linda
Schmidtobreick, Christophe Martayan, Patricia Guajardo and Manuel
Olivares.