We show that appealing to a Quark-Nova (QN) in a tight binary system containing a massive neutron star and a CO white dwarf (WD), a Type Ia explosion could occur. The QN ejecta collides with the WD driving a shock that triggers Carbon burning under degenerate conditions (the QN-Ia). The conditions in the compressed low-mass WD (M_WD < 0.9M_sun) in our model mimics those of a Chandrasekhar mass WD. The spin-down luminosity from the QN compact remnant (the quark star) provides additional power that makes the QN-Ia light-curve brighter and broader than a standard SN-Ia with similar 56Ni yield. In QNe-Ia, photometry and spectroscopy are not necessarily linked since the kinetic energy of the ejecta has a contribution from spin-down power and nuclear decay. Although QNe-Ia may not obey the Phillips relationship, their brightness and their relatively "normal looking" light-curves means they could be included in the cosmological sample. Light-curve fitters would be confused by the discrepancy between spectroscopy at peak and photometry and would correct for it by effectively brightening or dimming the QNe-Ia apparent magnitudes. Thus over- or under-estimating the true magnitude of these spin-down powered SNe-Ia. Contamination of QNe-Ia in samples of SNe-Ia used for cosmological analyses could systematically bias measurements of cosmological parameters if QNe-Ia are numerous enough at high-redshift. The strong mixing induced by spin-down wind combined with the low 56Ni yields in QNe-Ia means that these would lack a secondary maximum in the i-band despite their luminous nature. We discuss possible QNe-Ia progenitors.
Deep Dive into Quark-Novae in Neutron Star-White-Dwarf Binaries: A model for luminous (spin-down powered) sub-Chandrasekhar-mass Type Ia Supernovae ?.
We show that appealing to a Quark-Nova (QN) in a tight binary system containing a massive neutron star and a CO white dwarf (WD), a Type Ia explosion could occur. The QN ejecta collides with the WD driving a shock that triggers Carbon burning under degenerate conditions (the QN-Ia). The conditions in the compressed low-mass WD (M_WD < 0.9M_sun) in our model mimics those of a Chandrasekhar mass WD. The spin-down luminosity from the QN compact remnant (the quark star) provides additional power that makes the QN-Ia light-curve brighter and broader than a standard SN-Ia with similar 56Ni yield. In QNe-Ia, photometry and spectroscopy are not necessarily linked since the kinetic energy of the ejecta has a contribution from spin-down power and nuclear decay. Although QNe-Ia may not obey the Phillips relationship, their brightness and their relatively “normal looking” light-curves means they could be included in the cosmological sample. Light-curve fitters would be confused by the discrepancy
Despite their astrophysical significance, as a major contributor to cosmic nucleosynthesis and as distance indicators in observational cosmology, Type Ia supernovae (SNe-Ia) lack theoretical understanding. The evolution leading to explosion and its mechanisms are among the unknowns. The consensus is that type Ia supernovae result from thermonuclear explosions of carbon-oxygen (CO) white dwarfs (WDs; Hoyle & Fowler 1960;Arnett 1982). The explosion proper is generally thought to be triggered when the WD approaches (for accretion) or exceeds (for a merger) the Chandrasekhar mass, and the density and temperature become high enough to start runaway carbon fusion. Detonation models have been proposed for C-burning in the WD interior (Arnett 1969;Nomoto 1982) as well as deflagration models (Woosley & Weaver 1986). A delayed detonation transition (Khokhlov 1991a) may be needed to better replicate observations.
The nature of the progenitors of SNe-Ia is debated. Explosion models of SNe-Ia currently discussed in the literature include explosions of Chandrasekhar mass WDs and its variants (Khokhlov 1991b;Gamezo et al. 2005;Livne et al. 2005;Röpke & Niemeyer 2007;Jackson et al. 2010;Plewa 2007;Jordan et al. 2008;Meakin et al. 2009;Bravo et al. 2009 to cite only a few), explosion of super-massive WDs (e.g. Pfannes et al. 2010 and references therein), and of sub-Chandrasekhar WDs (Woosley et al. 1980;Nomoto 1982;Livne & Glasner 1991;Livne & Arnett 1995;Fink et al. 2010).
In the single degenerate (SD) scenario, if mass transfer is too slow, novae occur, which appear to remove as much mass as was accreted (Townsley & Bildsten 2004). If it is faster, H burns stably, but only a small range of accretion rate avoids expansion and mass-loss (Nomoto et al. 2007). The lack of H in spectra of SNe-Ia is often seen as troublesome for SD progenitor models. On the other hand, in the double-degenerate (DD) scenario, mergers of WDs could give rise to SNe-Ia (Webbink 1984;Iben& Tutukov 1984) and could naturally explain the lack of H. Both SD and DD scenarios may allow super-Chandrasekhar SNe-Ia. If the WD is spun up by accretion to very fast differential rotation (with mean angular velocity of order a few radians per second on average), then the WD may exceed the physical Chandrasekhar mass by up to some tenths of a solar mass before reaching explosive conditions in the central region (Yoon & Langer 2005). Merger simulations did not result in an explosion (e.g. Saio&Nomoto 2004) rather they indicate that an off-centre ignition causes the C and O to be converted to O, Ne, and Mg, generating a gravitational collapse rather than a thermonuclear disruption (Nomoto & Iben 1985). This is the so-called accretion-induced collapse (AIC) to a NS where C is not ignited explosively but quietly, yielding a faint explosion and a NS remnant instead of a SN-Ia (see also Stritzinger et al. 2005).
Theoretical and numerical (hydrodynamical) studies have previously shown that sub-Chandrasekhar mass WDs with an overlying helium shell (accreted from a companion) can undergo a double-detonation which could lead to a SN-Ia (Woosley et al. 1980;Nomoto 1982;Glasner & Livne 1990;Livne & Glasner 1991;Livne & Arnett 1995;Fink et al. 2007;Fink et al. 2010). In these models a layer of accreted helium (∼ 0.1-0.2M ⊙ ) is built either by burning accreted hydrogen to helium or by accretion of helium from a helium-rich donor (Woosley&Weaver 1986;Woosley&Weaver 1994;Ivanova&Taam 2004). When the pressure at the base of the helium layer reaches a critical threshold, it detonates driving a shock into the core of the WD. This causes a second detonation, resulting in a flame propagating outward from the core (or near it), destroying the WD. In edge-lit models, the mass of the WD must increase during the pre-supernova evolution to ∼ 0.9-1.1M ⊙ to explain typical SN-Ia luminosities (e.g. Woosley&Kasen 2011). This strong constraint on the WD mass is due to the fact that core densities > 2.5 × 10 7 g cm -3 are required for the detonation to produce enough radioactive Nickel (Sim et al. 2010) and to survive Nova-like outbursts at the high accretion rate which actually shrink the WD mass. Specifically, the WD mass should be at least 0.9 M ⊙ at the time of the SN-Ia (to produce an amount of 56 Ni within the range of normal SNe).
Although physically realistic, the double-detonation sub-Chandrasekhar model may suffer from the fact that even with a very low mass helium layer (∼ 0.05M ⊙ ) their spectroscopic signatures are not characteristic of observed SNe-Ia (Kromer et al. 2010; see also Ruiter et al. 2011). However, it has recently been argued that the model might be capable of producing a better match to observations, depending on details regarding the manner in which the accreted helium burns (e.g. Fink et al. 2010). It has also been suggested that a more complex composition of the helium layer may lead to a better agreement with observations but this remains to be confirmed. More
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