Core-collapse explosions of Wolf-Rayet stars and the connection to Type IIb/Ib/Ic supernovae

Abstract

We present non-LTE time-dependent radiative-transfer simulations of supernova\n(SN) IIb/Ib/Ic spectra and light curves, based on ~1B-energy piston-driven\nejecta, with and without 56Ni, produced from single and binary Wolf-Rayet (W-R)\nstars evolved at solar and sub-solar metallicities. Our bolometric light curves\nshow a 10-day long post-breakout plateau with a luminosity of 1-5x10^7Lsun. In\nour 56Ni-rich models, with ~3Msun ejecta masses, this plateau precedes a\n20-30-day long re-brightening phase initiated by the outward-diffusing heat\nwave powered by radioactive decay at depth. In low ejecta-mass models with\nmoderate mixing, Gamma-ray leakage starts as early as ~50d after explosion and\ncauses the nebular luminosity to steeply decline by ~0.02mag/d. Such\nsignatures, which are observed in standard SNe IIb/Ib/Ic, are consistent with\nlow-mass progenitors derived from a binary-star population. We propose that the\nmajority of stars with an initial mass ~<20Msun yield SNe II-P if 'effectively"\nsingle, SNe IIb/Ib/Ic if part of a close binary system, and SN-less black holes\nif more massive. Our ejecta, with outer hydrogen mass fractions as low as\n~>0.01 and a total hydrogen mass of ~>0.001Msun, yield the characteristic SN\nIIb spectral morphology at early times. However, by ~15d after the explosion,\nonly Halpha may remain as a weak absorption feature. Our binary models,\ncharacterised by helium surface mass fractions of ~>0.85, systematically show\nHeI lines during the post-breakout plateau, irrespective of the 56Ni abundance.\nSynthetic spectra show a strong sensitivity to metallicity, which offers the\npossibility to constrain it directly from SN spectroscopic modelling.\n