A Simple Approach to the Supernova Progenitor-Explosion Connection

Transcription

1 A Simple Approach to the Supernova Progenitor-Explosion Connection Bernhard Müller Queen's University Belfast Monash Alexander Heger, David Liptai, Joshua Cameron (Monash University)

2 Many potential/indirect observables from core-collapse supernovae, but some of the most direct ones (explosion energies, remnant masses) are challenging for SN theory! heavy elements massive star core-collapse supernovae gravitational waves neutrinos neutron stars & supernova remnants

3 The neutrino-driven mechanism in its modern flavour Heating or gain region develops some tens of ms after bounce Convective overturn & shock oscillations SASI enhance the efficiency of -heating, which finally revives the shock Big challenge: Show that this works! convection c ool ing Stalled accretion shock still pushed outward to ~150km as matter piles up on the PNS, then recedes again he atin g shock oscillations ( SASI ) shock

4 Status of 3D Neutrino Hydrodynamics Models with Multi-Group Transport First-principle 3D models: Mixed record, some failures Some explosions, delayed compared to 2D Models close to the threshold So what is missing? 27 M Hanke et al. (2013) 20 M Melson et al. (2015) 15 M Lentz et al. (2015) Or with simpler schemes: e.g. IDSA+leakage Takiwaki et al. (2014) L crit M M 2 3/ Ma 2 /3 3/ 5 Increase neutrino heating or Reynolds stresses Unknown/undetermined microphysics (e.g. Melson et al. 2015)? Lower explosion threshold in SASI-dominated regime (Fernandez 2015)? Better 1D/multi-D progenitor models?

5 Challenge: Connecting to Observables Janka et al. (2012) diagnostic explosion energy Several 1050erg with sustained accretion observations simulations accretion Pejcha & Prieto (2015): Explosion energies vs. Nickel masses outflow Hard to reach several 1050erg in many 2D simulations considerable accretion needed high neutron star masses Schwab & Podsiadlowski (2010): inferred neutron star birth mass distribution (beware selection effects...)

6 A Time-Scale Problem Explosion energies Müller (2015) Neutron star masses (baryonic) O'Connor & Couch (2015, submitted) bounce shock revival: ~a few 0.1s 1s Accretion can last well beyond 1s! explosion energy/neutron star mass determined

7 2D Long-Time Models not Adequate 2D 3D Shock trajectories Explosion energies Kelvin-Helmholtz instability suppressed Müller (2015) Long-time simulations with multi-group feasible in 2D but post-explosion dynamics is artificial (more than before explosion): Neutron star masses (baryonic) 3D accretion lasts too long, growth of explosion energy Long-time evolution in 2D: Cp. Raph Hix' inhibited question about the end of the explosion

8 Predicting Supernova Explosion Properties First-principle simulations vs. parameterised models 20 M Melson et al. (2015) Müller (2015) First-principle simulations: Physics captured as accurately as possible (neutrino transport, 3D effects, nuclear equation of state...) Cost: up to 50M core-h for 0.5s Systematic studies of explosion properties in 3D currently unfeasible Ugliano et al. (2012) Parameterised 1D hydro models:: Trigger explosion artificially (e.g. enhanced neutrino heating) Reasonably fast Require calibration: prediction or postdiction Explosions are not 1D

9 Recent Phenomenological Models Analytic + hybrid approaches (Fryer et al. 2012, Pejcha & Thompson 2015, Suwa et al. 2016) 1D simulations Regions of NS/BH formation: O'Connor & Ott (2010) Ugliano et al. (2012), Ertl et al. (2015), Sukhbold et al. (2015): grey transport + 1 or 2 calibration points Perego et al. (2015): PUSH extra heating by / -neutrinos in 1D Results Ugliano et al. (2012) O'Connor & Ott (2010): leakage + heating Variegated landscape of BH/NS formation above ~18M Empirical parameters for explodability (compactness, ErtlJanka criterion)

10 Why another parameterised model? How robust is the landscape of neutron star/black hole formation? (e.g. are the islands of NS/BH formation just due to stochastic variations in the progenitors) 1D hydro cannot capture simultaneous ejection and accretion ( important for energetics) Make connection to multi-d dynamics more manifest Quick tool for evaluating changes in stellar evolution models desirable Condense findings from recent multi-d models into a (largely) analytic approach?

11 Back from 3D to a Phenomenological Supernova Model Pre-Explosion Phase shock oscillations ( SASI ) Supersonic infall (~free-fall velocity) Shock: jump conditions shock convection Neutron star surface: contracting hard inner boundary 2 4/9 16/9 L E r NS 4 2 r sh 1 Ma 2/3 1/3 3 M M multi-d effects (see Müller & Janka 2015, Summa et al. 2015) Neutrino emission: L acc= GM M / 2R c ool ing he atin g Roughly hydrostatic, corrections from turbulent pressure L core E bind / t cool rsh, L, E... criticality parameter for explosive runaway time of shock revival & initial mass cut Still some free parameters, but these are physically relevant efficiency factors, time-scales, etc...

12 Explosion Phase de expl /dt h M out 2D 3D accretion M in outflow M out Total enthalpy Total energy Estimate end of accretion (Marek & Janka 2009): v post = 1 / v sh v esc M out Q ; Q = acc M in Shock velocity from formula of Matzner & McKee (1999) e bind,gain 1/ v E / M M / r sh expl ej ej E expl 6 Mev / mnucleon M out e bind,pre e burn M sh Estimate from pre-explosion phase growth of explosion energy, amount of residual accretion, neutron star mass (another >40 equations omitted, see Müller, Heger, Liptai & Cameron 2016, arxiv: )

13 Results Islands of explodability at high M>20 M8 (similar to previous work) Decent agreement with empirical explodability criteria, especially if we consider only shock revival: explosion energy Compactness parameter: 93% of models black hole mass Ertl criterion: 94% of models Obtainable with parameters compatible (by and large) with multi-d simulations neutron star mass Iron group elements Explosion properties for ~2000 KEPLER stellar evolution models: Islands of BH/NS formation are no statistical flukes

14 Results Islands of explodability at high M>20 M8 (similar to previous work) Decent agreement with empirical explodability criteria, especially if we consider only shock revival: Explosion energy vs. Nickel mass Compactness parameter: 93% of models Ertl criterion: 94% of models Observed correlation between MNi and Eexpl (Hamuy 2003) and Mej and Eexpl (Poznanski 2013, Chugai & Utrobin 2014, Pejcha & Prieto 2015) red/blue: fits to observational date from Pejcha & Prieto (2015) Explosion energy vs. ejecta mass Affected by fallback?

15 Work left for everyone... Explosion energy vs. Nickel mass Corridor of 0.3dex in Nickel mass: Estimate from analytic model is shaky (based on ignition temperatures) 1D hydro needed for more reliable Ni mass & detailed nucleosynthesis Explosion energy vs. ejecta mass Correlation of Eexpl and Mej Clump of low-energy explosions at high Mej due to lack of fallback treatment? ( 1D/multi-D hydro) How robust are the observed correlations? red/blue: fits to observational date from Pejcha & Prieto (2015) fallback?

16 Is this landscape robust? exp: shock compression ratio affects post-shock velocity and termination of accretion turb: shock expansion due to turbulent stresses affects critical luminosity for explosion Parameter variations largely tantamount to rescaling of Eexpl and Mni and/or shift of boundaries between NS/BH formation regions underlying landscape of explodability & potentially attainable energies is robust (exception: change in neutron star cooling time)

17 Conflicts: Upper mass limit for NS formation? turb=1.15, expl=3 Looks not too bad Very high NS masses BH formation above ~19M8 can be accommodated with plausible parameter choices but conflict with NS mass distribution & GCE (cp. Falk Herwig's talk)? Some of the observational constraints may be soft (selection effects for NS masses,...) but tensions still warrant explanation Observations (Schwab & Podsiadlowski 2010) mainly NS/NS binaries Cumulative distribution function of inferred progenitor masses from Smartt (2015)

18 Conclusions & Outlook Analytic model for explosion properties directly from progenitor structure? strength: simple model for simultaneous accretion/ejection weakness: no good fallback model, etc. Complementary approach to previous 1D models Findings largely corroborate parametric 1D models but extent of BH/NS can't be pinned down precisely Natural explanation for Mej-Eexpl correlation (cp. Nakamura et al in 2D) little change in explodability Suggests our 3D models will go in the right direction once we can compute long enough... How to better capture multi-d hydro in phenomenological models (SASI, seed perturbations)? How to reconcile different observational constraints (from light curve/spectral modelling, progenitor observations, remnant masses, GCE) with each other?