Type Ia Supernovae Progenitors

Type Ia Supernovae Historical defining characteristics: Generally, lack of lines of hydrogen Contain a strong Si II absorption feature (6355Å shifted to ~6100Å)

Observational Characteristics Homogeneity: nearly 60% homogeneous in terms of spectra, light curves, peak absolute magnitudes M B ~ log(H o /74) Inhomogeneity: differences in spectra, light curves, do exist. In terms of explosion strength, order: Very weak, e.g. SN 1991bg, SN 1992k Weak, e.g. SN 1986G Normal, ~60% Very bright, e.g. SN 1991T, ~20%

Energy:½(~10 4 km/s) 2 ~ E CO->Fe Degeneracy:Explosive event Spectrum:Generally no hydrogen Delay:Explosions can occur with long delay after cessation of star formation. Basic model:Thermonuclear disruption of mass-accreting white dwarf. Note:Flame physics is still an unsolved problem, deflagration to detonation? The following simple facts

Why is identifying the progenitors so important? The fact that we still don’t know the progenitors of some of the most dramatic explosions – a major embarrassment. For dark energy properties we need to understand the evolution of the luminosity with cosmic time. Feedback – radiative, kinetic, nucleosynthetic input into galaxy evolution.

Form at M wd ≲ 0.45M ☉ Can explode at ∼ 0.7M ☉ central He ignition But composition of ejected matter: He + 56 Ni + decay products Inconsistent with observations Form from M ∼ M ☉ But not numerous enough and expected to collapse to NS rather than explode Composition of accreting WD O-Ne-MgC-OHe Yes No

At what mass does the WD explode? Chandrasekhar mass carbon igniters Carbon ignites at center: Sub-Chandra mass helium igniters 1.At ~10 51 ergs Ni decay powers lightcurve 3.X; (V j ) consistent with spectra 4.M Ch explains homogeneity 1.Difficult to reach M Ch 2.For M WD ≳ 1.2M ☉ collapse to NS rather than explosion may ensue Indirect double detonation or “edge lit” detonation One detonation propagates outward (through He), inward pressure wave compresses the C-O, ignites off center, followed by outward detonation. +−

At what mass does the WD explode? Composition of high velocity ejecta In sub-Chandra mass WDs Intermediate mass elements sandwiched by Ni and He/Ni rich High velocity Ni, He! No high velocity C!

For progenitors we have two possible scenarios Double degenerate Merger of two CO WDs brought together by gravitational radiation Single degenerate A CO WD accretes material from a main sequence or red giant companion Binary WD systemsSystems such as: Recurrent novae Supersoft x-ray sources Symbiotic systems

Evolutionary Scenarios

Double degenerate scenario Strengths 1.Population synthesis predicts the right statistics. 2.Double degenerate systems detected observationally. 3.Mergers with some significant consequences appear inevitable. 4.In ellipticals, consistent with observed x-ray flux (~30x smaller than predicted for SDS). Weaknesses 1.Off-center carbon ignition may lead to O- Ne-Mg WD and accretion induced collapse rather than SN Ia.

Double degenerate scenario 1.The merger of two 0.9 M ☉ WDs produced a subluminous SN Ia (SN 1991bg-like).

Double degenerate scenario 2.Simulation of 0.6 M ☉ M ☉ suggested that SNe Ia could be obtained if

Single degenerate scenario Strengths 1.If accreted matter can be retained, natural path to increasing mass. 2.Candidate progenitors exist. Weaknesses 1.It is not absolutely clear that a hydrogen-accreting WD can indeed reach M Ch. 2.Limits on the presence of H exclude symbiotics with the highest mass loss rates. 3.In ellipticals, the observed x-ray flux ~30x smaller than predicted.

A few recent observational findings 1.Two populations: “Prompt” – SN Ia rate ~ star formation rate “Delayed” – SN Ia rate ~ stellar mass ⇓ a.Rate higher in late type galaxies. b.For higher z prompt dominate sample. c.Prompt are brighter.

Recent observational findings 2.A decrease with redshift in the strength of intermediate mass element features (consistent with higher brightness, which implies larger mass of 56 Ni).

Recent observational findings 3.The luminosity-weighted age of the host galaxy is correlated with the 56 Ni yield ⇒ more massive progenitors give rise to more luminous explosions.

Recent observational findings 4.Super-Chandrasekhar mass progenitors? E.g. SNLS-03D3bb SN 2009dc.

Serendipity and SNe Ia A short (10 sec) acquisition image by STIS on board HST of the nucleus of the radio-loud galaxy 3C 78 revealed a point source superposed very near the jet – a SN Ia.

Possibility to Increase SNe Ia Rate? The shocks produced by jets can either: a.Heat mass-donor star in binaries containing white dwarfs, thereby increasing the mass transfer rate. or b.Compress clumps in the interstellar medium thereby increasing the mass accretion rate onto low-velocity white dwarfs. Prediction: The rate of classical novae should increase too, because novae are obtained when white dwarfs accrete at rates

Serendipity and Classical Novae An HST program intended to measure the proper motion of the optical jet in M87 discovered 11 transient sources in the vicinity of the jet. HST WFPC2

Conclusions 1.Single degenerate scenario could, in principle, explain everything: prompt are caused by accretion from young main sequence stars (~8M ☉ ), and delayed are caused by accretion from red giant companions (~1M ☉ ). However, models involve maybe too many “moving parts.”

Conclusions 2.Double degenerates could perhaps produce SNe Ia, especially in ellipticals, but many uncertainties remain. 3.Is there something to be learned from gamma-ray bursts? In particular, if indeed both double degenerates and single degenerates contribute to SNe Ia, then it would be hard to believe that mergers and accretion from a red giant, in ellipticals, would appear precisely the same in all two- parameter diagrams (e.g., the separation between long and short GRBs in duration-hardness diagrams). Consequently, there should be some phase space in which the two progenitor families should separate.