http://arxiv.org/abs/1509.07124
We present the first systematic investigation of spectral properties of 17 Type Ic Supernovae (SNe Ic), 10 broad-lined SNe Ic (SNe Ic-bl) without observed Gamma-Ray Bursts (GRBs) and 10 SNe Ic-bl with GRBs (SN-GRBs) as a function of time in order to probe their explosion conditions and progenitors. We analyze a total of 396 spectra, which were drawn from published spectra of individual SNe as well as from the densely time-sampled spectra data of Modjaz et al. (2014). In order to quantify the diversity of the SN spectra as a function of SN subtype, we construct average spectra of SNe Ic, SNe Ic-bl without GRBs and SNe Ic-bl with GRBs, along with standard deviation and maximum deviation contours. We find that SN~1994I is not a typical SN Ic, in contrast to common belief, while the spectra of SN 1998bw/GRB 980425 are representative of mean spectra of SNe Ic-bl. We measure the ejecta absorption and width velocities (as traced by FeII 5169) and find that SNe Ic-bl with GRBs, on average, have quantifiably higher absorption velocities, as well as broader line widths than SNe without observed GRBs. We interpret this to indicate that SNe Ic-bl without observed GRBs may have had lower energy, chocked jets that imparted lower velocities to the SN ejecta. Moreover, we address the He-problem in SNe Ic-bl, namely whether the puzzling lack of He lines in SN Ic-bl spectra could be due to their He lines being too broadened by the high velocities present, and thus smeared out. We show that the absence of clear He lines in optical spectra of all SNe Ic-bl, and in particular of SN-GRBs, is not due to them being too smeared out. This implies that the progenitor stars of SN-GRBs are probably He-free, in addition to being H-free, which puts strong constraints on the stellar evolutionary paths needed to produce such SN-GRB progenitor stars at the observed low metallicities. (Abridged)
M. Modjaz, Y. Liu, F. Bianco, et. al.
Fri, 25 Sep 15
20/56
Comments: Comments: Submitted to ApJ. 24 pages, 11 figures, 6 Tables, Appendix. Comments welcome
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