GRB 171205A: Detection of the emerging SN

ATel #11038; A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), L. Izzo, D. A. Kann, C. C. Thoene (all HETH/IAA-CSIC), P. Pesev, R. Scarpa, and D. Perez (all GTC) report on behalf of a larger collaboration:
on 7 Dec 2017; 19:18 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: David Alexander Kann (kann@tls-tautenburg.de)

Subjects: Optical, Gamma-Ray Burst, Supernovae

We have been monitoring the counterpart of GRB 171205A (D'Elia et al. GCN #22177; 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-lined Ic supernova.

Further information will be provided through the TNS.