Ultra-stripped supernovae: progenitors and fate

Abstract

The explosion of ultra-stripped stars in close binaries can lead to ejecta masses < 0.1 M ⊙ and may explain some of the recent discoveries of weak and fast optical transients. In Tau ris et al. (2013), it was demonstrated that helium star companions to neutron stars (NSs) may experience mass transfer and evolve into naked ∼ 1.5 M ⊙ metal cores, barely above the Chandrasekhar mass limit. Here we elaborate on this work and present a systematic investigation of the progenitor evolution leading to ultra-stripped supernovae (SNe). In particular, we examine the binary parameter space leading to electron-capture (EC SNe) and iron core-collapse SNe (Fe CCSNe), respectively, and determine the amount of helium ejected with applications to their observational classification as Type Ib or Type Ic. We mainly evolve systems where the SN progenitors are helium star donors of initial mass M He = 2.5 − 3.5 M ⊙ in tight binaries with orbital periods of P orb = 0.06 − 2.0 days, and hosting an accreting NS, but we also discuss the evolution of wider systems and of both more massive and lighter -as well as single -helium stars. In some cases we are able to follow the evolution until the onset of silicon burning, just a few days prior to the SN explosion. We find that ultra-stripped SNe are possible for both EC SNe and Fe CCSNe. EC SNe only occur for M He = 2.60 − 2.95 M ⊙ depending on P orb . The general outcome, however, is an Fe CCSN above this mass interval and an ONeMg or CO white dwarf for smaller masses. For the exploding stars, the amount of helium ejected is correlated with P orb -the tightest systems even having donors being stripped down to envelopes of less than 0.01 M ⊙ . We estimate the rise time of ultra-stripped SNe to be in the range 12 hr − 8 days, and light curve decay times between 1 and 50 days. A number of fitting formulae for our models are provided with applications to population synthesis. Ultrastripped SNe may produce NSs in the mass range 1.10 − 1.80 M ⊙ and are highly relevant for LIGO/VIRGO since most (possibly all) merging double NS systems have evolved through this phase. Finally, we discuss the low-velocity kicks which might be imparted on these resulting NSs at birth.

Neutrino-driven explosions of ultra-stripped Type Ic supernovae generating binary neutron stars

“…It is quite difficult to relate between ZAMS mass and CO-core mass in binary systems because mass transfer proceeds very complicatedly during the evolution. On He star-NS binaries, He stars with MHe 3.5M⊙ and with the initial orbital period of P orb 0.5d have an evolutional path to ultra-stripped SNe (Tauris et al 2015). These He stars evolved to CO cores with MCO 1.8M⊙ surrounded by very thin He envelope.…”

“…One of the possible candidates for a SN forming a close binary system is ultra-stripped SN (Tauris et al 2015), which would launch peculiar type Ib/c SN with a faint and fast decaying light curve. Peak luminosity of Type Ib/c SNe is determined primarily by the ejected mass of 56 Ni, M56 Ni , while the timescale around the peak is determined by the diffusion timescale τc ∝ M 3/4 ej E −1/4 K , where Mej is the ejecta mass and EK is the kinetic energy of the ejecta (Arnett 1982).…”

“…For instance, type Ic SN 2005ek is one of these SNe (Drout et al 2013;Tauris et al 2013), whose estimated ejecta mass, ∼ O(0.1)M⊙ is notably smaller than typical SN Ic, O(1)M⊙ (Drout et al 2011), as well as smaller 56 Ni mass, and the explosion energy is also smaller by an order of magnitude (O(10 50 ) erg) than typical core-collapse SNe (O(10 51 ) erg). To model these rapidly-evolving SNe with small ejecta mass, the progenitor stars are thought to be stripped much more than canonical stripped-envelope type Ib/c SNe, that is, ultra-stripped SNe coined by Tauris et al (2013); Tauris et al (2015). Besides SN 2005ek and other known SNe, ten rapidly-evolving transients were recently detected by Pan-STARRS1, which exhibit shorter decay-ing timescale (∼ 10 days) than canonical SNe with peak barometric luminosities ranging from ∼ 10 42 to 10 43 erg s −1 (Drout et al 2014).…”

Explosive Nucleosynthesis of Ultra-Stripped Type Ic Supernovae

“…Ultra-stripped supernovae (SNe) could be a generation site of binary compact objects such as binary neutron stars (NSs) [1,2]. The evolutionary channels to form these binary systems such as the standard channel and the double-core channel were discussed in e.g., [3].…”

“…The evolutionary channels to form these binary systems such as the standard channel and the double-core channel were discussed in e.g., [3]. Close binary systems forming ultra-stripped Type Ic SNe would result in very close system of compact objects so that the merging of these objects will occur within cosmic age [2] and provide r-process elements (e.g., [4]). Fast-fading faint Type Ic SN 2005ek [5] is considered to belong to ultra-stripped SNe [1].…”