Type Ia supernovae have two physical width–luminosity relations and they favour sub-Chandrasekhar and direct collision models – I. Bolometric

Abstract

While the width-luminosity relation (WLR) among type Ia supernovae (slower is brighter) has been extensively studied, its physical basis has not been convincingly identified. In particular, the 'width' has not been quantitatively linked yet to a physical time scale. We demonstrate that there are two robust fundamental time scales that 1. can be calculated based on integral quantities of the ejecta, with little dependence on radiation transfer modeling and 2. can be inferred from observations. The first is the gamma-ray escape time t 0 , which determines the long-term evolution of the bolometric light curve and is studied in this Paper I. The second is the recombination time of 56 Fe and 56 Co, which sets the long-term color evolution of the emitted light and is studied in Paper II. Here we show that the gamma-ray escape time t 0 can be derived with ∼ 15% accuracy from bolometric observations based on first principles. When applied to a sample of supernovae, the observed values of t 0 span a narrow range of 30 − 45 days for the wide range of observed 56 Ni masses 0.1M ⊙ M56 Ni 1M ⊙ . This narrow range of the gamma-ray escape time across the range of luminosities (a trivial WLR) is consistent with central detonations and direct collisions of sub-Chandrasekhar mass white dwarfs (WDs) but not with delayed detonation models for explosions of Chandrasekhar mass WDs, which are therefore disfavored as the primary channel for the population of type Ia supernovae. Computer codes for extracting t 0 from observations and models and for calculating gamma-ray transfer in 1D-3D are provided.

Properties of Type-Ia Supernova Light Curves

“…For the 16 remaining events, the ratio falls in a narrow range centered around t B /t d ≈ 1.65, consistent with the calculations presented in Fig. 6. and is in excellent agreement with the range measured in Wygoda et al (2019). This agreement suggests that t γ can be estimated without integration on bolometric measurements; instead a simple estimate of the peak time (i.e.…”

Radioactive Heating Rate of r-process Elements and Macronova Light Curve

“…t 0 (Swartz et al 1995;Jeffery 1999;Wygoda et al 2019). This time scale, t 0 , is defined by the time at which the effective optical depth for γ-rays is unity, τ γ,eff = 1:…”

Evidence for Late-stage Eruptive Mass Loss in the Progenitor to SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient

“…Thus on this scale it seems that M Ni ∼ 0.3 M , similar to other Ic-BL SNe (Lyman et al 2016). Because the data have not yet converged to model tracks, we cannot solve directly for t 0 and M Ni using the technique for Ia SNe in Wygoda et al (2019).…”

“…To estimate the nickel mass of AT2018cow,Perley et al (2019a) compared the bolometric luminosity at t ∼ 20 day to that of SN2002ap (whose nickel mass was derived via late-time nebular spectroscopy;Foley et al 2003) and found M Ni < 0.05 M . On this scale, we would expect M Ni 0.05 M for SN2018gep as well.Finally,Katz et al (2013) andWygoda et al (2019) present an analytical technique for testing whether a light curve is powered by radioactive decay. At late times, the bolometric luminosity is equal to the rate of energy deposition by radioactive decay Q(t), because The bolometric light curve of SN2018gep compared to (left) other Ic-BL SNe from the literature(Cano 2013) and (right) to AT2018cow(Perley et al 2019a).…”