Diversity in Type Ia Supernovae:White Dwarf Collisions as a possible

SNe Ia Channel Friedrich-K. Thielemann (Basel)

but research done by Domingo Garcia-Senz (Barcelona), Ruben Cabezon (Basel), Almudena

Arcones (Darmstadt), A. Relano (Barcelona)

From an old guy: a bit of Pre-History

Pioneering Ideas: electron-degenerate cores (Hoyle & Fowler 1960), Carbon-detonations (Arnett 1969, but inconsistent with observed abundances) Observational Constraints: H-deficient stars (Oke & Searke 1974), only SNe in elliptical galaxies (Tammann 1974), not concentrated in spiral arms (Maza & van den Bergh1976), exponential tail of light curves (Barbon et al. 1973), detailed (light curve) observations of 1972e (Kirshner & Oke 1975), Ni-Co-Fe in spectra (Meyerott 1980), Branch (1982,1984) saw Ca,Si,S,Mg,O and Co at v

exp=10 000km in 1981b...., the differences between the SNe I

subclasses became just clear or recognized.Theoretical Conclusions and Models: Exploding white dwarfs (Finzi & Wolf 1967, Whelan & Iben 1973), energy source 56Ni (Arnett 1979, Colgate et al. 1980, Axelrod 1980, Weaver, Axelrod, Woosley 1980, Chevalier 1981, Trimble 1982, Wheeler 1982), He white dwarfs (Arnett 1971, Mazurek 1973, Nomoto & Sugimoto 1977, Wheeler 1978, Arnett 1979),He-accreting white dwarfs (Nomoto & Sugimoto 1977, Fujimoto & Sugimoto 1979, 1981, Taam 1980, Nomoto 1980, 1981, Woosley, Weaver & Taam 1980, Sugimoto & Miyaj 1981, Fujimoto & Sugimoto 1982)Options: Single detonations, double detonations, central carbon deflagrations (Ivanova, Imshennik & Chechetkin 1974, instabilities and convective propagation: Buchler & Mazurek 1975, Nomoto, Sugimoto & Neo 1976, Müller & Arnett 1982, 1984, Sutherland & Wheeler 1984)

In all cases: the white dwarf burns via combustion and 12C+12C ignition!

Supernova classification

Filippenko 1997

Observers introduced the terms type I and II dependent on the observation of H-lines (absorption), but there seemed to be a wide variety of type I's a, b, c (discovered in early 80s).One finds type II's and Ib/c's in regions of recent star formation and none of them in elliptical galaxies (no recent star formation) => massive stars with H/He envelope lost.In elliptical galaxies, i.e. without recent star formation, only type Ia's are found (rejuvenated binaries?)!

Single and Double Detonations and other Options Nomoto 1982

If assumung He-accreation !! discarded in those days, He-detonations gave abundance features in the outer layers inconsistant with observations

Type Ia Supernovae: Accretion in Binary Stellar Systems

binary systems with accretion onto one compact object can lead (depending on accretion rate) to explosive events with thermonuclear runaway (under electron-degenerate conditions)- white dwarfs (novae, type Ia supernovae = called single degenerate )- neutron stars (type I X-ray bursts, superbursts?)

Accretion History and Outcome (old ideas): Nomoto 1982a,b, Nomoto & Kondo 1991

H-accretion He-accretion

the accretion rate determines whether pile-up (and explosive ignition) or steady burning. Until recently ignition of He-detonations seemed to give abundance features in the outer layers inconsistant with observations.

Central Ignition

for three different accretion ratesNomoto, Thielemann, Yokoi 1984

ignition when C-fusion energy exceeds neutrino losses

In spherical symmetry, such ignitions can be followed in a self-consistentmanner with the aid of an implicit Lagrangian hydro-code

Back of the Envelope SN Ia (Fowler & Hoyle 1960)

P. Höflich

W7 deflagrations (Nomoto, Thielemann, Yokoi 1984); delayed detonations (Khokhlov, Höflich, Müller; Woosley et al.)

in spherically symmetric models description of the burning front propagation (with hydrodynamic instabilities) determines outcome!

Explosive Burning

typical explosive burning process timescale order of seconds: fusion reactions (He, C, O) density dependent (He quadratic, C,O linear)photodisintegrations (Ne, Si) not density dependent

O C Ne Si

Explosive Burning

complete expl. Si-burning with alpha-rich freeze-out

detailed analysis Thielemann, Nomoto & Yokoi 1986

T9

t(s)

Explosive Si-Burning

Explosive Burning above a critical temperature destroys (photodisintegrates) all nuclei and (re-)builds them up during the expansion. Dependent on density, the full NSE is maintained and leads to only Fe-group nuclei (normal freeze-out) or the reactions linking 4He to C and beyond freeze out earlier (alpha-rich freeze-out).

W7

T9,p

“historical” understanding (W7, Nomoto, Thielemann, Yokoi et al. 1984)

56Fe

56Ni

54Fe

NSE

a deflagration (subsonic burning front) with a propagation speed related (initially) to heat conduction and (later) to mixing via Rayleigh-Taylor instabilities (treated in time-depen-dent mixing length theory of 0.7 times the pressure scale height). Y

e in inner zones determined by electron capture (electrons degenerate with high

Fermi energy), in outer zones by metallicity (-> 54Fe, 58Ni).

Metallicity Effects

W7 W70

Iwamoto, Brachwitz et al. (1999); Ye in outer zones made by initial 22Ne

H-burning CNO->14N, He-burning 14N(α,γ)18F(β+)18O(α,γ)22Ne

(a) Test for influence of new shell model electron capture rates (including pf- shell Langanke, Martinez-Pinedo 2003)(b) Test for burning front propagation speed (Brachwitz et al. 2001, Thielemann et al. 2004) ign. densities 2,4,6,8x109gcm-3, B1,B2 deflagration speeds direct influence on dominant Fe-group composition resulting from SNe Ia

54Fe, 58Ni

56Ni

56Fe

50Ti,54Cr

Fuller, Fowler, Newman (FFN)

Langanke, Martinez-Pinedo

Role of large shell model calculations for e-capture on Fe-group nuclei and role of deflagration speeds / ignition

densities

Ignition density determines Ye and neutron-richness of (60-70% of) Fe-group

results of explosive C, Ne, O and Si-burning:Fe-group to alpha-elements 2/1-3/1

SNe Ia dominate Fe-group, over-abundances by more than factor 2 not permitted maximum centraldensity 3 109 gcm-3

FKT et al. (2004, spher. sym. explosions with parametrized burning front)

48Ca, 50Ti, 54Cr .. strong indicators!!

„for the discovery of the accelerating expansion of the Universe through observations of distant supernovae“

(these searches led to large surveys with huge data base for SNe Ia)!

Saul Perlmutter (UC Berkeley), Head of Supernova Cosmology ProjectBrian Schmidt (Australian National University), Adam Riess (Johns Hopkins Univ.), Head and main analyzer of High-z Supernova SearchTeam (both grad. students of Bob Kirshner, Harvard, PhD in 93 and 96)

SN Ia Correlations

days past B maximum

Log L

(erg/s)

Leibundgut ESO

SN Ia Correlations

Luminosity vs. decline rate• Phillips 1993, Hamuy et al. 1996, Riess et al. 1996, 1998, Perlmutter et

al. 1997, Goldhaber et al. 2001

Luminosity vs. rise and decline time• Riess et al. 1999

Luminosity vs. color at maximum• Riess et al. 1996, Tripp 1998, Phillips et al. 1999

Luminosity vs. line strengths and line widths• Nugent et al. 1995, Riess et al. 1998, Mazzali et al. 1998

Luminosity vs. host galaxy morphology• Filippenko 1989, Hamuy et al. 1995, 1996, Schmidt et al. 1998, Branch

et al. 1996

If real luminosity L (erg/s) known and observed intensity l (erg/s cm2) measured, they are related via L=4π d2 l, i.e. the (luminosity) distance could be determined!

Subluminous Type Ia Supernovae

from Taubenberger (2008), ∆m15

(B)true

of these SNe is given in parenthesis

opacity

Ni massexplosion energy

Ni distribution

Pinto and Eastman (2000)

We need to know 56Ni mass in the explosion from peak luminositytotal mass of the explosion anddistribution of the ashes of the explosion (Ni and intermediate mass elements)differences in the explosion energies

Nickel masses of SNe IaSN MB log(L) M(Ni)

SN1989B -19.37 43.06 0.57SN1991T -19.76 43.23 0.84SN1991bg -16.78 42.32 0.11SN1992A -18.80 42.88 0.39SN1992bc -19.72 43.22 0.84SN1992bo -18.89 42.91 0.41SN1994D -18.91 42.91 0.41SN1994ae -19.24 43.04 0.55SN1995D -19.66 43.19 0.77

Contardo et al. 2000; data for SN 1991 from Strolger et al. 2002

Leibundgut (ESO)

Zorro diagram

The distribution of the main abundance groups in a sample of SNe Ia. The enclosed mass of di erent burning products is plotted ffvs. ∆m15 (B).Open circles refer to stable 54Fe and 58Ni; solid circles to 56Ni, and open triangles to the sum of these. Crosses show the mass enclosed inside the layer of intermediate mass elements (IME), i.e., the total mass burned.54Fe and 58Ni in the SN core are roughly constant over all luminosities,while 56Ni determines the luminosity and correlates with ∆m15 (B). The mass enclosed by the position of IME's is inferred to be similar for all SNe of the sample, and the explosion energy seems constant (from Mazzali et al. 2007).

Hillebrandt et al. (2013)

(Fe-group elements)

Multiple Sub-Classes of SNe Ia

Taken from Sim (2012): what are the origins of these different Sub-classes????

Don Lamb on Branch-normal, Chandrasekhar mass models

Present and future 3D modelsconsistent treatment needed instead of parametrized spherical propagation, MPA Garching/Würzburg (Röpke et al.), U. Chicago/ SUNY Stony Brook (Calder et al.)- distribution of ignition points uncertain (deflagration, centrally ignited delayed detonation, off-center delayed detonation)- hydrodynamic instabilities determine propagation- deflagration/detonation transition

Explicit hydro-codes cannot handle transition to thermonuclear runaway => assumed ignitionconditions

Seitenzahlet al. 2013

Attempts to overcome constraints of explicit 3D hydrocodes

low Mach number hydrodynamics algorithms filter soundwaves from the system, allowing for the efficient simulation of long timescale processes (not constrained by Courant condition,permitting only timesteps of the sound crossing time between gridpoints). Zingale (2013, Maestro code), showing energy generation in convective region during simmering phase before SN Ia explosion. Slightly off-centerignition likely in a single point!?

Variations in Type Ia models• Double Detonations: central detonations of Chandrasekhar mass WDs give wrong nucleosynthesis features, this is the reason why a deflagration pre-expansion is needed. Detonations of sub-Chandrasekhar mass WDs with lower central densities avoid this, but an ignition has to be caused artificially. This might occur during accreation instabilities of the unburned He-shell before it attains its regular (detonation) ignition mass. If the He-layer can be minimized before He (double-)detonations the outcome could be consistant with observations (Bildsten et al. 2007, Kromer et al. 2010, Sim et al. 2010)

From Sim (2012)3D version with He-detonation, causingcompression and central C-ignition

White Dwarf Collisions/Mergers: This scenario was already long discussed (Webbing 1984, Iben & Tutukov 1984). First real simulations by Benz et al. (1989), but discarded as it would only work in head-on collisions. Recent population studies (Dan et al. 2011, Katz & Dong 2012) show that this could be an (although infrequent) pathway to type Ia supernovae in galactic centers and globular clusters, where the statistics for such collisions is high. High resolution 3D calculations by e.g. Rosswog et al. (2009), Raskin et al. (2009, 2010), Pakmor et al. (2010, 2012), Hawley et al. (2012)

Hydrodynamic evolution and thermonu-clear explosion of a WD merger pair of 1.1 and 0.9 M☉ (Pakmor et al. 2012). Initially the WDs orbit each other with a period of 35 s. After a few orbits the ∼secondary is tidally disrupted and collides with the more massive primary reaching densities and temperatures su cient to ffiignite a detonation at 610 s (black cross). At 612 s the detonation front (black line) hasburned almost the complete object. Color-coded is the logarithm of the density0.64 M☉ 56 Ni0.6 M intermediate-mass elements 0.47 M☉ O 0.09 M☉ C remain

.

☉

Comparison of synthetic spectra with SN 2005cf(from Hillebrandt et al. 2013)

(i) single-degenerate delayed-detonation Röpke et al. (2012), (ii) sub-Chandrasekhar-mass double detonations Kromer et al. (2010), (iii) a double-degenerate WD merger (1.1 + 0.9 M, Pakmor et al. (2012)

Models for superluminous SNe Ia?

from Sim (2012)

Delayed ignition due to reduced densities caused by centrifugal forces

High resolution simulations of the head-on collision ofwhite dwarfs

D. Garcıa-Senz, R.M. Cabezon , A. Arcones, A. Relano, F.-K. Thielemann

The direct impact of white dwarfs has been suggested as a plausible channel for type Ia supernovae in highly populated globular clusters and in galactic centers, where the amount of white dwarfs is considerable and the rate of violent collisions non-negligible. There are indications that binary white dwarf systems orbited by a third stellar-massbody have an important chance to induce a clean head-on collision. This scenario represents a source of contamination for the supernova light-curve samples used as standard candles in cosmology, and it deserves further investigation.We present the results of high resolution hydrodynamical simulations jointly with a detailed nuclear post-processing, to check the viability of white dwarf collisions to produce significant amounts of 56Ni with a 2D-axial symmetric SPH code to obtain a resolution considerably higher than in previous studies. We also study how the initial mass and composition a ect the results. ff The gravitational wave emission is also calculated, as a unique signature of this kind of events. All calculated models produce a significant amount of 56Ni, ranging from 0.1-1.1M☉ , compatible not only with normal-Branch type Ia supernova but also with subluminous and super-Chandrasekhar objects. The distribution mass-function of white dwarfs favors collisions among 0.6 −0.7 M☉ objects, leading to subluminous events (with 2D 40 km resolution).

Variety of Simulations:initial conditions relate to totalinitial energy at infinity = 0

0.7 +0.7

1.06 + 0.81

Detailed Abundances

Comparison of existing models for head-on collisions

Head-on collisions pollute regular SNe Ia (Branch normal) sample; statistics of population synthesis required; can (opposite to mergers) also produce superluminous objects !