[vsnet-grb-info 17330] GRB 151215A: NOT spectroscopy and redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18696
SUBJECT: GRB 151215A: NOT spectroscopy and redshift
DATE:    15/12/15 10:15:44 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

D. Xu (NAOC/CAS), N. R. Tanvir (Univ. Leicester), D. Malesani 
(DARK/NBI), J. P. U. Fynbo (DARK/NBI), P. Jakobsson (Univ. Iceland), J. 
Saario (NOT and Univ. Turku) report on behalf of a larger collaboration:

We observed the optical afterglow (Cenko, GCN 18692; Wiseman et al., GCN 
18694) of GRB 151215A (Gibson et al., GCN 18691) using the Nordic 
Optical Telescope (NOT) equipped with the AlFOSC camera and spectrograph.

The optical afterglow is clearly visible in our images, and we measure 
its brightness on Dec 15.160 UT (0.81 hr after the GRB) to be R = 20.07 
+- 0.02 (Vega, assuming R = 16.31 for the USNO star at RA = 06:14:19.93, 
Dec = +35:31:06.0).

A sequence of three spectra of 1200 s each was carried out starting on 
Dec 15.176 UT (1.2 hr after the trigger), covering the wavelength range 
3200-9000 AA.

A wide trough is visible superimposed on the afterglow continuum, 
indicating Lyalpha absorption from neutral hydrogen. We also detect 
several narrow absorption features, which we interpret as due to, e.g., 
Si II, O I, Al II, all at a common redshift of z = 2.59. A preliminary 
fit to the Lyalpha profile yields an HI column density of 3x10^21 cm^-2, 
though establishing the system as a DLA.