TITLE:   GCN CIRCULAR
NUMBER:  14798
SUBJECT: GRB 130606A: MMT Spectroscopy
DATE:    13/06/07 05:16:26 GMT
FROM:    Ryan Chornock at Harvard  <rchornock@cfa.harvard.edu>

R. Lunnan, M. Drout, R. Chornock, and E. Berger (Harvard) report:

We observed the optical afterglow (Jelinek et al., GNC 14782; Xu et al., GCN 
14783; Nagayama et al., GCN 14784; Virgili et al., 14785; Masi et al., GCN 
14789; Leonini et al., GCN 14791; Sonbas et al., GCN 14797) of GRB 130606A 
(Ukwatta et al., GCN 14781) using the Blue Channel spectrograph on the 6.5-m MMT 
starting at 04:04 UT on 7 June (7.0 hours after the BAT trigger).  We obtained 
4x1200s of spectroscopy spanning the wavelength range 7450-9350 Angs with a 
resolution of 2.1 Angstroms.

We detect a sharp cutoff in flux blueward of ~8425 Angs, consistent with 
Lyman-alpha at a redshift of z=5.9, with very little transmission between 7850 
and 8400 Angs, although some flux is present blueward of that.  Several metal 
absorption lines are present to the red, including NV, Si II, C II, and O I at 
redshift z=5.913, confirming the GTC redshift of Castro-Tirado et al. (GCN 
14790, GCN 14796).