Radiative Transfer Modelling of Core-Collapse Supernovae (RTCCSN)

Luc Dessart (LAM) and Stéphane Blondin (CPPM)

Abstract: Core-collapse supernovae (CCSNe) are among the most luminous objects in the Universe. They chemically enrich the interstellar medium, especially in oxygen, and thus make the material of life. Through their energetic explosions they deposit kinetic and radiation energy into the interstellar/intergalactic medium. This complicated process can both trigger and inhibit star formation. Furthermore, all CCSNe give birth to a compact remnant, a neutron star or a stellar-mass black hole. For a small subset of these, the supernova is accompanied by a long-duration -ray burst (LGRB). Such LGRBs are thought to follow the formation of a rapidly rotating black hole in a Wolf-Rayet (WR) star progenitor characterised by a fast-rotating and massive pre-SN iron core. Hence, massive stars and their explosive deaths are key actors in the local and distant Universe. This proposal aims at studying these still enigmatic events, to better understand their massive-star origin and the processes by which they explode.

We propose to conduct a comprehensive study of CCSN spectra and light curves (LCs) using the state-of-the-art 1-D non-LTE time-dependent radiation-transfer code CMFGEN. The goals are manifold but rest fundamentally on modelling SN light to better constrain massive-star evolution, massive star explosions, and promoting the use of CCSNe for cosmology through the determination of distances in the Universe.

Our work will be based on massive-star progenitors resulting from the single as well as the binary evolution channel, at both low, solar, and high environmental metallicities, and encompass a wide range of main-sequence masses. Using our radiation-hydrodynamics code V1D (Livne 1993; Dessart et al. 2010ab) and the large database of pre-SN models publicly available, we will artificially generate SN ejecta by mimicking the explosion through the deposition of thermal energy, or by driving a piston, at the base of the progenitor envelope.

We will then remap such ejecta onto CMFGEN (Hillier 1990; Hillier & Miller 1998; Dessart & Hillier 2005ab,2008,2010a) and compute the evolution of the gas and radiation with full allowance for non-Local-Thermodynamic-Equilibrium (non-LTE), time-dependent terms in the radiative-transfer, energy, and statistical-equilibrium equations, and non- thermal processes induced by radioactive decay of unstable isotopes produced in the explosion.

Our limitation to 1D allows us to computationally handle these important non-LTE, time-dependent, and non-thermal effects, and thus reach a high level of physical consistency unmatched in the supernova community today. Using this procedure, we successfully modelled key radiative properties of the brightest CCSN observed to date, SN1987A in the LMC, as well as other CCSNe associated with red-supergiant (RSG) or WR star explosions. We now wish to extend these studies to explore a wider range of progenitors, progenitor- model origin, and a wider range of explosion properties (energy, nucleosynthesis, mixing).

Our calculations will provide the largest existing database of synthetic CCSN LCs and spectra, with ~300 time sequences and a total of ~15000 spectra, which we will compare to observations, either existing or obtained through a collaborative program with the University of California at Berkeley (UCB, collaborator Alex Filippenko). A key asset of this proposal is physical consistency through the successive use of stellar-evolutionary models and stellar explosion models for a detailed radiative-transfer modelling performed on the full ejecta, and continuously from the early-time photospheric phase until the late-time nebular phase.

This end-to-end approach will foster a better understanding of these still elusive events, massive-star evolution, the CCSN explosion mechanism, and the connection to LGRBs. It will also prepare for forthcoming deep blind wide-angle transient surveys like LSST.