Supernova Explosions of Super-asymptotic Giant Branch Stars: Multicolor Light Curves of Electron-capture Supernovae

An electron-capture supernova (ECSN) is a core-collapse supernova (CCSN) explosion of a super-asymptotic giant branch (SAGB) star with a main-sequence mass M _MS ~ 7-9.5 M _⊙. The explosion takes place in accordance with core bounce and subsequent neutrino heating and is a unique example successfully produced by first-principle simulations. This allows us to derive a first self-consistent multicolor light curve of a CCSN. Adopting the explosion properties derived by the first-principle simulation, i.e., the low explosion energy of 1.5 × 10⁵⁰ erg and the small ⁵⁶Ni mass of 2.5 × 10^-3 M _⊙, we perform a multi-group radiation hydrodynamics calculation of ECSNe and present multicolor light curves of ECSNe of SAGB stars with various envelope masses and hydrogen abundances. We demonstrate that a shock breakout has a peak luminosity of L ~ 2 × 10⁴⁴ erg s^-1 and can evaporate circumstellar dust up to R ~ 10¹⁷ cm for the case of carbon dust, that the plateau luminosity and plateau duration of ECSNe are L ~ 10⁴² erg s^-1 and t ~ 60-100 days, respectively, and that a plateau is followed by a tail with a luminosity drop by ~4 mag. The ECSN shows a bright and short plateau that is as bright as typical Type II plateau supernovae, and a faint tail that might be influenced by the spin-down luminosity of a newborn pulsar. Furthermore, the theoretical models are compared with ECSN candidates: SN 1054 and SN 2008S. We find that SN 1054 shares the characteristics of the ECSNe. For SN 2008S, we find that its faint plateau requires an ECSN model with a significantly low explosion energy of E ~ 10⁴⁸ erg.