Radiative-transfer models for explosions from rotating and non-rotating single WC stars - Implications for SN?1998bw and LGRB/SNe

摘要

Using 1D, non-local thermodynamic equilibrium and time-dependent radiative transfer simulations, we study the ejecta properties required to match the early- and late-time photometric and spectroscopic properties of supernovae (SNe) associated with long-duration γ -ray bursts (LGRBs). Matching the short rise time, narrow light curve peak and extremely broad spectral lines of SN?1998bw requires a model with ? 3? M _(⊙) ejecta but a high explosion energy of a few 10 ~(52) ?erg and 0.5? M _(⊙) of ~(56)Ni . The relatively high luminosity, presence of narrow spectral lines of intermediate mass elements, and low ionisation at the nebular stage, however, are matched with a more standard C-rich Wolf-Rayet (WR) star explosion, an ejecta of ? 10? M _(⊙) , an explosion energy ? 10 ~(51) ?erg, and only 0.1? M _(⊙) of ~(56)Ni . As the two models are mutually exclusive, the breaking of spherical symmetry is essential to match the early- and late-time photometric and spectroscopic properties of SN?1998bw. This conclusion confirms the notion that the ejecta of SN?1998bw is highly aspherical on large scales. More generally, with asphericity, the energetics and ~(56)N i masses of LGRB/SNe are reduced and their ejecta masses are increased, favouring a massive fast-rotating Wolf-Rayet star progenitor. Contrary to persisting claims in favour of the proto-magnetar model for LGRB/SNe, such progenitor/ejecta properties are compatible with collapsar formation. Ejecta properties of LGRB/SNe inferred from 1D radiative-transfer modelling are fundamentally flawed.