Neutrinos in supernova evolution and nucleosynthesis

Transcription

1 Neutrinos in supernova evolution and nucleosynthesis Gabriel Martínez Pinedo International School of Nuclear Physics 39th Course Neutrinos in Cosmology, in Astro-, Particle- and Nuclear Physics Erice, Sicily, September 16-24, 2017

2 Outline 1 Introduction 2 Neutrinos in supernova Muons and their impact in supernova explosions Nucleosynthesis in neutrino-driven winds Neutrino nucleosynthesis 3 Neutrinos and neutron star mergers Impact on electromagnetic transients 4 Summary

3 Introduction Neutrinos in supernova Neutrinos and neutron star mergers Summary Core-collapse supernova H.-Th. Janka, et al, PTEP 01A309 (2012) "!

4 Relevant neutrino processes Many different neutrino processes need to be modelled within Boltzmann radiation transport. CC β-processes CC scattering process e ν e e + ν e ν e, ν e e, e + W +, W W +, W W +, W p, (A,Z) n, (A,Z 1) n p e, e + ν e, ν e NC scattering processes (ν = νe, νe, νμ, νμ, ντ, ντ) ν ν ν ν ν ν Z 0 Z 0 Z 0 n, p, (A,Z) n, p, (A,Z) e, e + e, e + ν ν Neutrino-pair ( thermal ) processes e e + e ν Z 0 ν ν e W +, W n, p n, p Z 0 π ν ν n, p n, p γ γ ν e Z 0 e + ν ν e e W +, W ν e ν e Z 0 ν μ, ν τ νμ, ντ e + νe e + ν e From H.-Th. Janka, arxiv: [astro-ph.he]

5 Microphysics vs multidimensional supernova Three dimensional supernova simulations are very sensitive to variations of 10-20% in neutrino opacities (Melson+, 2015) Most studies focus on neutral current neutrino-nucleon scattering: 1 dσ V dω G2 F E2 [ ] ν c 2 16π 2 a (3 cos θ)s A + c 2 v(1 + cos θ)s V Reduction due to strangeness contribution to axial-vector coupling constant (Melson+, 2015, Hobbs+, 2016): c a = ±g A g s, g s = ± Reduction structure factor due to correlations at low densities (Virial expansion Horowitz+, 2017) What about additional degrees of freedom: muons, pions, hyperons,...

6 Muons in core-collapse supernova Muons are routinely considered in cold neutron stars but so far have been neglected in supernova modeling. Muons can be produced both by thermal (electromagnetic) processes and by weak processes.

7 Description of muon opacities Thermal processes (subdominant) ν + µ ν + µ ν + µ + ν + µ + ν µ + e ν e + µ ν µ + e + ν e + µ + ν µ + ν e + e µ ν µ + ν e + e + µ + ν e + e ν µ + µ ν e + e + ν µ + µ + ν µ + n p + µ ν µ + p n + µ + γ + γ µ + + µ e + + e µ + + µ weak processes: produce a net muonic number. Requires six flavor Boltzmann neutrino transport. A. Lohs, 2015

8 Introduction Neutrinos in supernova Neutrinos and neutron star mergers 2D simulations Inclusion of muons can lead to explosions in models that otherwise do not explode Radius [km] Radius [km] tpb [s] Bollig, Janka,Lohs, GMP, Horowitz, and Melson, arxiv: [astro-ph.he] Summary

9 Composition around 400 ms Thermal energy is converted into muon rest mass energy Electron degeneracy pressure reduced Net Y e,µ [10 1 /by] Density [g/cm 3 ] electrons muons Standard Muons Muons+Strangeness+Virial ν e Anti ν e ν µ Anti ν µ Density Temperature Radius [km] Y ν [10 1 /by] Temperature [MeV]

10 2D simulations: shock evolution Inclusion of muons favors the explosion Protoneutron star shrinks faster Strangeness corrections also favor explosions Role of virial correlations uncertain. R(shock) [km] R(ρ=10 11 g/cm 3 ) [km] Standard Virial Muons Muons+Virial Muons+Strangeness+Virial t pb [s] t pb [s] Mass accretion rate [M O /s] Gain layer heating [B/s]

11 2D simulations: neutrino spectral properties Hotter neutrino emission with distinct neutrino spectra for all flavors. L(ν e ) [B/s] <ε>(ν e ) [MeV] t pb [s] ν e Anti ν e ν µ Anti ν µ t pb [s] ν τ Anti ν τ t pb [s] L(ν µτ ) [B/s] <ε>(ν µτ ) [MeV]

12 Neutrino-driven winds and r process 10 5 Neutrino cooling and Neutrino-driven wind Woosley et al, ApJ 433, 229 (1994), suggested neutrino-driven winds as the r-process site. R in km Ni Si νe,µ,τ, νe,µ,τ 10 2 Rns ~10 νp-process r-process He O 1.4 α, p α, p, nuclei n, p α, n α, n, nuclei Abundance νe,µ,τ, νe,µ,τ Rν PNS M(r) in M 3 Mass Number

13 Nucleosynthesis in neutrino-driven winds Neutrino interactions determine Y e ν e + n p + e ν e + p n + e + Neutron-rich ejecta: [ ] E νe E νe > 4 np L νe [ ] L νe 1 E νe 2 np neutron-rich ejecta: weak r-process proton-rich ejecta: νp-process Energy difference related to symmetry energy (GMP+ 2012, Roberts+ 2012) 1D Boltzmann transport simulation (DD2 EoS) Luminosity [erg/s] heνi [MeV] Electron fraction 0.46 GMP ν e ν- e ν x Time [s]

14 Nucleosynthesis Neutron-deficient isotopes of elements between Zn and Mo Rel. abundance Elemental abundance Mass number A Can heavier elements be produced? HD Charge number Z Improved treatment opacities: no, increases Y e. Explosions lighter stars (ONeMg cores): yes, reduced exposure to neutrino fluxes. Flavor oscillations: Collective: minor impact (Wu+ 2015) Active-sterile ( m as 1 ev): important impact on nucleosynthesis, detrimental for the explosion (Nunokawa+ 1997, Wu+ 2013)

15 MSW mechanism for sterile neutrinos For the case of active (electron neutrinos)-sterille flavor conversions. The ν e effective potential is: 2 Vν eff e = 2 G ρ F (c e m vy e + cv p Y p + c n vy n ) = 3 ( 2 u 2 G ρ F Y e 1 ) 3 The MSW resonance for neutrinos will appear when: m 2 cos 2θ = 3 ( 2 2E ν 2 G ρ F Y e 1 ) Vν eff 3 e Y e = ɛ m u and for antineutrinos: m 2 cos 2θ = 3 2 2E ν 2 G ρ F m u m u ( Y e 1 ) V ν eff 3 e Y e = 1 3 ɛ Oscillations depend on Y e -profile that is itself affected by the oscillations. A fully self-consistent approach is necessary to account for feedback effects Feedback effects enhance oscillations and reduce Y e of ejected matter.

16 Impact on nucleosynthesis M.-R. Wu, T. Fischer, GMP, Y.-Z. Qian, PRD 89, (R), 2014 Y e (a) t pb (ms) Elemental abundance (b) Atomic number, Z Active-sterile flavor conversion increases the neutron richness of the ejected material This allows for the production of elements between Sr and Cd in agreement with metal-poor star observations.

17 Neutrino nucleosynthesis: ν process Neutrino-nucleus interactions in the outer layers produce several key isotopes (Woosley+ 1990, Heger+ 2005, Suzuki+ 2013) Product Parent Reaction 7 Li 4 He 4 He(ν, ν p) 3 H(α, γ) 7 Li He(ν, ν n) 3 He(α, γ) 7 Be(e, ν e ) 7 Li 11 B 12 C 12 C(ν, ν n) 11 C(β + ) 11 B, C(ν, ν p) 11 B 15 N 16 O 16 O(ν, ν n) 15 O(β + ) 15 N, O(ν, ν p) 15 N 19 F 20 Ne 20 Ne(ν, ν n) 19 Ne(β + ) 19 F, Ne(ν, ν p) 19 F 138 La 138 Ba 138 Ba(ν e, e ) 138 La, Ba(ν e, e n) 137 La(n, γ) 138 La 180 Ta 180 Hf 180 Hf(ν e, e ) 180 Ta So far studies have assumed large average neutrino energies: E νe = 12 MeV, E νe = 15.8 MeV, E νµ,τ = 19 MeV (high energies) Modern supernova simulations predict lower average energies: E νe = 9 MeV, E νe = 12 MeV, E νµ,τ = 12 MeV (low energies)

18 Nucleosynthesis yields Yields normalized to 16 O and averaged over initial mass function. Nucleus no ν Low energies High energies 7 Li B N F La Ta Li and 15 N varely produced by the ν process 11 B consistent with expected yields from cosmic rays (Austin+ 2011) 19 F is expected to be produced mainly in AGB stars 138 La and 180 Ta have also contributions from s process. 138 La 180 Ta 7 Li 11 B 19 F 15 N Yields (M ) high energies low energies without neutrinos Main sequence mass (M ) Sieverding+, in preparation

19 Merger channels and ejection mechanism In mergers we deal with a variety of initial configurations (netron-star neutron-star vs neutron-star black-hole) with additional variations in the mass-ratio. The evolution after the merger also allows for further variations. NSNS wind; t~100 ms dyn. ejecta; t~ 1 ms torus unbinding; t ~ 1s BH formation sgrb NSBH Rosswog, et al, Class. Quantum Gravity 34, (2017)

20 Introduction Neutrinos in supernova Neutrinos and neutron star mergers Summary Kilonova/Macronova electromagnetic transient Electromagnetic transitent from radioactive decay r-process ejecta [Li & Paczyn ski 1998] Luminosities 1000 times those of a nova at timescales of a day in the blue [Metzger et al, 2010] Large optical opacities of Lanthanides delay the peak to timescales of a week in the red/infrared [Kasen et al, 2013] Probably observed associated to GRB B Time since GRB B (d) m X-ray F606W 22 F160W 1.6 m N E First direct observation of an r-process event? Time since GRB B (s) Tanvir+, Nature 500, 457 (2013) X-ray flux (erg s 1 cm 2) 5 AB magnitude 23

21 r process and electromagnetic transient Provided sufficiently neutron rich matter is ejected Y e 0.1 (merger neutron star black hole) a robust r process takes place L bol (ergs s 1 ) FRDM DZ Days Luminosity is mainly sensitive to abundances of long-live actinides that release energy by alpha-decay. Mendoza-Temis, Wu, Langanke, GMP, Bauswein, Janka, PRC 92, (2015) Barnes, Kasen, Wu, GMP, ApJ 829, 110 (2016); Rosswog et al, CQG 34, (2017)

22 Introduction Neutrinos in supernova Neutrinos and neutron star mergers neutrinos in NS-NS mergers For NS-NS mergers the central hypermassive neutron star will produce large neutrino fluxes Lν 1053 erg s 1 (Sekiguchi+ 2015, 2016). Mildly neutron-rich ejecta in the polar region (Ye. 0.5). Lanthanide free ejecta. From Y. Sekiguchi et al, PRD 93, (2016). Summary

23 Observational consequences An observation of a light curve from a NS-NS from the polar region it is expected to produce a blue kilonova on timescales of a day. At later times red/infrared emission from neutron-rich ejecta may dominate. We may even see a signature of the collapse of the hypermassive neutron star to a black hole. luminosity t ~day? t ~week time Disk Outflow Ye ~ OR HMNS Disk Dynamical Ejecta Y e < 0.1 From Metzger & Fernández, MNRAS 441, 3444 (2014)

24 Summary Muon production in supernova matter facilitates neutrino-driven explosions. Heavy element nucleosynthesis in core-collapse supernova is limited to elements between Zn and Mo (A 90). Neutron star mergers are likely the site where the main r process takes place. Radioactive decay of r-process ejecta produces an electromagnetic transient known as kilonova. The observation of a kilonova transient will confirm that r process occurs in mergers and provide information about the dynamics and the role of neutrinos.