Electron-capture supernovae exploding within their progenitor wind

Abstract

The most massive stars on the asymptotic giant branch (AGB), or the so-called super-AGB stars, are thought to produce supernovae triggered by electron captures in their degenerate O+Ne+Mg cores. Super-AGB stars are expected to have slow winds with high mass-loss rates, so their circumstellar density is high. The explosions of super-AGB stars are therefore presumed to occur in this dense circumstellar environment. We provide the first synthetic light curves for such events by exploding realistic electron-capture supernova progenitors within their super-AGB winds. We find that the early light curve -that is, before the recombination wave reaches the bottom of the hydrogen-rich envelope of supernova ejecta (the plateau phase) -is not affected by the dense wind. However, after the luminosity drop following the plateau phase, the luminosity remains much higher when the super-AGB wind is taken into account. We compare our results to the historical light curve of SN 1054, the progenitor of the Crab Nebula, and show that the explosion of an electron-capture supernova within an ordinary super-AGB wind can explain the observed light curve features. We conclude that SN 1054 could have been a Type IIn supernova without any extra extreme mass loss, which was previously suggested to be necessary to account for its early high luminosity. We also show that our light curves match Type IIn supernovae with an early plateau phase or the so-called Type IIn-P supernovae, and suggest that they are electron-capture supernovae within super-AGB winds. Although some electron-capture supernovae can be bright in the optical spectral range due to the large progenitor radius, their X-ray luminosity from the interaction does not necessarily get as bright as other Type IIn supernovae whose optical luminosities are also powered by the interaction. Thus, we suggest that optically bright X-ray-faint Type IIn supernovae can emerge from electron-capture supernovae. Optically faint Type IIn supernovae, such as SN 2008S, can also originate from electron-capture supernovae if their hydrogen-rich envelope masses are small. We argue that some of them can be observed as Type IIn-b supernovae due to the small hydrogen-rich envelope mass.

The Remarkable Deaths of 9–11 Solar Mass Stars

“…Despite these computational challenges, the late stages of evolution of these stars have been studied extensively. Representative historical and important recent calculations have been done by Miyaji et al (1980), Hillebrandt et al (1984), Nomoto (1984Nomoto ( , 1987, Mayle & Wilson (1988), Dominguez et al (1993), Timmes et al (1994), Gutierrez et al (1996), Garcia-Berro et al (1997), Iben et al (1997), Ritossa et al (1999), Siess (2006), Poelarends et al (2008), Jones et al (2013Jones et al ( , 2014, Takahashi et al (2013), Tauris et al (2013Tauris et al ( , 2015, Doherty et al (2015), and Moriya et al (2014).…”

“…Even a small fraction of the integrated convective luminosity during the last ten years would be sufficient to eject the entire envelope. The interaction of the supernova shock with a dense wind could also appreciably brighten the event (Moriya et al 2014). …”

New expansion rate measurements of the Crab nebula in radio and optical

“…We note here, however, that there is an alternate interpretation, which is that SN 1054 was a low-energy electroncapture event, with only a small ejected mass, and that the presently visible filaments are the result of the PWN interacting with the circumstellar material (Smith 2013;Tominaga et al 2013;Moriya et al 2014). The progenitor in this case is expected to have been a super-asymptotic giant branch star, in other words one at the upper end of the mass range of the asymptotic giant branch, with a mass of around 8 to 10 M ⊙ , although the mass is not well constrained (see Moriya et al 2014, and references therein).…”

“…Smith 2013; Tominaga et al 2013; Moriya et al 2014), interaction of the supernova shock with the circumstellar medium (CSM) was responsible for the luminosity of SN 1054 as well as for the presently visible filaments, which contain largely swept-up CSM rather than supernova ejecta. The PWN is therefore confined by the dense wind from the super-asymptotic giant branch progenitor of the supernova.…”

“…The progenitor in this case is expected to have been a super-asymptotic giant branch star, in other words one at the upper end of the mass range of the asymptotic giant branch, with a mass of around 8 to 10 M ⊙ , although the mass is not well constrained (see Moriya et al 2014, and references therein). Such progenitors are expected to produce slow, dense winds before the SN explosion.…”