[vsnet-grb-info 17037] GRB 150915A: VLT/X-shooter redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18318
SUBJECT: GRB 150915A: VLT/X-shooter redshift
DATE:    15/09/16 07:51:37 GMT
FROM:    Valerio D'Elia at ASDC  <delia at asdc.asi.it>

V. D'Elia (ASI/ASDC and INAF-OAR), T. Kruehler (MPE), D. Xu (NAOC/CAS), Pall Jakobsson (Univ. Iceland), N. R. Tanvir (U. Leicester), A. de Ugarte Postigo (IAA/CSIC), D. Malesani (DARK/NBI) and J. P. U. Fynbo (DARK/NBI), report on behalf of a larger collaboration:

We observed the optical counterpart of GRB 150915A (D'Elia et al., GCN 18315) with the ESO VLT equipped with the X-shooter spectrograph. Four spectra with individual exposure time of 1200 s were secured covering the wavelength range 3,000-21,000 AA. Spectroscopy began 3.3 hr after the BAT trigger. The afterglow is well detected in our acquisition image at the position of the optical counterpart (Yates et al., GCN 18317).

We detect a number of absorption features at a common redshift of z = 1.968, including Ly-a, C IV, Al II, Si II, Fe II, Mg II. We also detect fine-structure lines at the same redshift (e.g. FeII* 2396 / 2389, and Si II* 1533). Finally, we report strong emission lines of [O II], H-alpha and H-beta at a similar redshift, thus confirming z=1.968 as the GRB/host galaxy redshift.

We thank the kind assistence of the observing staff at Paranal, in particular Steve Ertel.