A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), L. Izzo (HETH/IAA-CSIC),
D.A. Kann (HETH/IAA-CSIC), C.C. Thoene (HETH/IAA-CSIC), P. Pesev (GTC),
R. Scarpa (GTC), D. Perez (GTC) report on behalf of a larger collaboration:
We have been monitoring the counterpart of GRB 171205A (D'Elia et al.
GCN22177; Izzo et al., GCN 22180) photometrically and spectroscopically
with OSIRIS at the 10.4m GTC telescope. Our latest observation consisted of
3x600s exposure using the R1000B grism, which covers the spectral range
between 3700 and 7880 Angstrom. On the combined spectrum, with epoch on
the 7th of December at 6:05 UT, we detect broad undulating spectral features,
which are prominent between 4000 and 6000 Angstrom, superposed to the
afterglow continuum, which seem to indicate the emergence of an underlying
supernova component. The features include a double bump in this range,
similar to what was seen for the very early spectra of SN 1998bw (Patat et al.
2001), indicating that this is probably also a broad line Ic supernova.
Further information will be provided through the TNS.