2017/07/09 by Fengwu Sun, A. Gal‐Yam, Sun, Fengwu +1
Physics and Astronomy · #FOS: Physical sciences #Gamma-ray bursts and supernovae #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · pdf · doi:10.48550/arxiv.1707.02543
openalex publication_date 2017/07/09 · openalex created_date 2017/07/21 · openalex updated_date 2026/07/28
We present a set of new quantitative classification criteria for major subclasses of Type I Supernovae (SNe). We analyze peak spectra of 146 SNe Ia from the Berkeley Supernova Ia Program (BSNIP), 12 SNe Ib, 19 SNe Ic (including 5 SNe Ic-BL) and 4 SNe Ib/c. All the spectra are within 5 days of maximum light. We study their absorption line depths relative to the pseudo-continuum at around observed wavelength 6150Å, attributed to Si II 6355Å for SNe Ia and Ic and to hydrogen for SNe Ib, and O I λ7774Å observed around λ7500Å. We found that Type I SNe could be quantitatively classified using the line depths at these two absorption regions. Type Ia SNe, including normal SNe Ia, Ia-1991bg and Ia-1999aa, show strong signatures of Si II near peak with relative line depth values of a\rm (λ6150Å)>0.35. Only SNe Ia-2002cx (Iax) do not satisfy this criterion, while the a\rm (O I λ7774Å) index can separate SNe Ia-1991bg and Ia-1999aa cleanly. Type Ib SNe satisfy that a\rm (λ6150Å)<0.35 and a\rm (λ6150Å) / a\rm (O I λ7774Å)>1, while regular Type Ic SNe show a\rm (λ6150Å)<0.35 but a\rm (λ6150Å) / a\rm (O I λ7774Å)<1. These quantitive classification criteria work well for the majority of normal Type I SN subclasses. Peculiar SNe Ia-2002cx and SNe Ic-BL are the exception. We apply these criteria to provide clear identifications to intermediate or unclear SNe Ib/c. The results show good consistency with classification using specific spectral line features. Though there are still some puzzles about the physical mechanisms driving the diverse line ratios, our method is an accurate empirical method to identify the majority of Type I SNe.