[vsnet-grb-info 16799] GRB 150727A: VLT/X-shooter redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18080
SUBJECT: GRB 150727A: VLT/X-shooter redshift
DATE:    15/07/28 05:14:42 GMT
FROM:    Nial Tanvir at U.Leicester  <nrt3 at star.le.ac.uk>

N. R. Tanvir (U. Leicester), D. Xu (NAOC/CAS), T. Zafar (ESO), S. Covino (INAF/OABr), S. Schulze (PUC, MAS) report for a larger collaboration:

We observed the afterglow of GRB 150727A (Cenko et al. GCN 18076) with VLT/X-shooter, beginning at 2015-07-28 00:01 UT, about 5 hr after the burst.

Preliminary analysis of the spectrum reveals emission lines of Halpha, Hbeta and [OIII] 4959/5007 at a redshift of z=0.313. There is only marginal evidence of the [OII] 3727 doublet, suggesting the emission lines are coming from a dust obscured region (consistent also with a high Ha:Hb ratio). The continuum is faint with no clear absorption lines, but can be traced in the blue as far as the instrumental cut-off at about 3100A. Despite the absence of detected absorption features, it is likely that the emission lines are from the host galaxy and therefore that this redshift is also that of the GRB.