[vsnet-grb-info 17157] GRB 151027B: VLT/X-shooter redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18506
SUBJECT: GRB 151027B: VLT/X-shooter redshift
DATE:    15/10/28 06:35:40 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu at nao.cas.cn>

D. Xu (NAOC/CAS), N. R. Tanvir (U. Leicester), D. Malesani, J. P. U. 
Fynbo (DARK) report on behalf of a larger collaboration:

We observed the optical afterglow of GRB 151027B (Ukwatta et al. GCN 
18499, Malesani et al. GCN 18501) with the VLT X-shooter spectrograph 
covering a spectral range 3400A to 18000A. Observations began at 2015 
Oct 28 03:50 UT, approximately 5h09m post-burst.

The spectrum shows a clear continuum in the red, with a strong break 
corresponding to Ly-alpha at a redshift of z=4.063.  This is supported 
by detection of absorption lines corresponding to Si II 1259/1260, Si 
II* 1265, CII 1335, CII* 1336, OI 1302, SiII 1304, S IV 1394/1403, CIV 
1548/1551 and Al II 1671 at that redshift. We therefore propose this as 
the redshift of the GRB.

We thank the staff at Paranal, particularly T. Rivinius and I. Condor, 
for their support in obtaining these observations.