A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), C.C. Thoene (IAA-CSIC),
J. Gorosabel (IAA-CSIC, UPV/EHU), R. Sanchez-Ramirez (IAA-CSIC),
G. Leloudas (OKC, Stockholm), Z. Cano (U. Iceland), D. Xu (DARK/NBI),
K. Wiersema (U. Leicester), J.P.U. Fynbo, D. Malesani, J. Hjorth (DARK/NBI),
P. Jakobsson (U. Iceland), O.E. Hartoog (U. Amsterdam) report on behalf of
a larger collaboration:
We have observed the optical counterpart of GRB 130215A (D'Elia et al.,
GCN 14204, Zheng et al., GCN 14205) with the 10.4 m GTC telescope
equipped with the OSIRIS imager and spectrograph. A spectroscopic
observation was performed on 12 March 2013 at a mean time of 20:52 UT,
25.8 days after the burst, corresponding to 16.2 days after the burst in the
rest frame, considering a redshift of z=0.597 (Cucchiara et al. GCN 14207).
The total exposure was 3x1200s using a low resolution grating (R~600)
covering a wavelength range 5000-10000 A. Due to its current location,
observations had to be carried out at high airmass, between 1.6 and 2.2.
There were thin cirrus but seeing was very good, at 0.6".
At this epoch, the spectrum presents undulations typical of SN spectra,
including a prominent bump at ~8200 A. Using SNID (Blondin & Tonry 2007,
ApJ, 666, 1024), we have compared the spectrum to a series of SN templates.
The spectrum gives a good match to a number of SNe Ic, including
broad-lined and normal events such as SN 2002ap and SN 1994I, around
maximum light or slightly after. By leaving the redshift unconstrained we
obtain the same template fit and derive a redshift of z=0.58+/-0.02, fully
consistent with the absorption line redshift.
We acknowledge excellent support from the GTC staff, in particular
Carlos A. Alvarez Iglesias.