Supernova neutrinos - KVIloehner/saf_seminar/2010/supernova-neutrinos.pdf · Introduction Core-collapse SN1987AProspectsConclusions Supernova neutrinos Ane Anema November 12, 2010

Introduction Core-collapse SN1987A Prospects Conclusions

Supernova neutrinos

Ane Anema

November 12, 2010

Introduction Core-collapse SN1987A Prospects Conclusions

Outline

1 Introduction

2 Core-collapse

3 SN1987A

4 Prospects

5 Conclusions

Introduction Core-collapse SN1987A Prospects Conclusions

Types of supernovae

Figure: Classification (figure 15.1, Giunti)

Introduction Core-collapse SN1987A Prospects Conclusions

Supernova rates

Figure: Rates (figure 15.2, Giunti)

Upper bound on supernovae in Milky Way

13 supernovae per century 90% CL.

Introduction Core-collapse SN1987A Prospects Conclusions

Mass versus metallicity

Figure: Supernovae type, mass and metallicity (figure 15.5, Giunti)

Introduction Core-collapse SN1987A Prospects Conclusions

Interior structure of massive star

Figure: Interior structure (figure 15.6, Giunti)

Table: Burning phases for 15M�star (table 15.2, Giunti)

Phase Time scale (yr)

H 1.11 · 107

He 1.97 · 106

C 2.03 · 103

Ne 0.732O 2.58Si 5.01 · 10−2

Introduction Core-collapse SN1987A Prospects Conclusions

Collapse

Iron core

Mc ∼ 1.26M�, Rc ∼ 103 km, pc ∼ 1010 g cm−3, Tc ∼ 1 MeV.

1 The iron core contracts.

2 Temperature of core increases, so

γ + 56Fe→ 13α + 4n − 124 MeV.

3 Electron capture

e− + N (Z ,A)→ N (Z − 1,A) + νe

e− + p → n + νe

4 Number of electrons in core decreases. Neutrinos are emitted.

Introduction Core-collapse SN1987A Prospects Conclusions

Collapse

Chandrasekhar limit

The electron gas pressure must counteract gravity.

M . 5.83Y 2e M� where Ye =

Np

Np + Nn

5 Fewer electrons implies lower Chandrasekhar limit.

6 Iron core collapses under gravitational pressure.7 Photodissociation and electron capture rates increase.

〈Eν〉 ≈ 12− 16 MeV,L ≈ 1053 erg s−1 ≈ 1020 L�,E ≈ 1051 erg ≈ 10−3 M�.

8 Neutrinos get trapped in inner core (1011 g cm−3).

9 Nucleon gas halts collapse of inner core (1014 g cm−3, t ≈ 1s).

Introduction Core-collapse SN1987A Prospects Conclusions

Proto-neutron star

Proto-neutron star

Inner core has

density 1014 g cm−3,radius 10 km.

Outer core has

density & 109 g cm−3,radius 100 km.

Introduction Core-collapse SN1987A Prospects Conclusions

Shock wave

10 Outward propagating shock wave arises (100km ms−1).

11 Nuclei are dissociated by shock wave.

12 Behind shock wave protons capture electrons.13 Shock breakout (1011 g cm−3). Release of neutrinos

L ≈ 6 · 1053 erg s−1 ≈ 6 · 1020 L�,E ≈ 1051 erg ≈ 10−3 M�,time scale: a few milliseconds.

14 Shock wave weakens by photodissociation.

Introduction Core-collapse SN1987A Prospects Conclusions

Shock wave

Scenarios

Shock wave blows away outer layers of progenitor.

Shock wave halts. Black hole due to accumulated mass.

Shock wave stalls, but is revived by

convection behind shock wave,oscillations of proto-neutron star,thermal neutrinos.

Energy released during collapse

Neutrinos carry away 99% of the 3 · 1053 erg of gravitationalenergy released.

Introduction Core-collapse SN1987A Prospects Conclusions

Cooling phase

Core of proto-neutron star has temperature of 40 MeV.

Pair annihilatione− + e+ → ν + ν̄

Bremsstrahlung

e± + N → e± + N + ν + ν̄

N + N → N + N + ν + ν̄

Plasmon decayγ → ν + ν̄

Photoannihilation

γ + e± → e± + ν + ν̄

Introduction Core-collapse SN1987A Prospects Conclusions

Neutrinosphere

Inner region of proto-neutron star is opaque to neutrinos.

Neutrinosphere is outer region of proto-neutron star notopaque to neutrinos.

Neutrinosphere depends on flavour and energy of neutrino.

both νe and ν̄e interact via charged and neutral current,other neutrinos only via neutral current.

Radius of neutrinosphere about 50-100 km.

Opacities for νe , ν̄e different due to few protons in outer core

ν̄e + p → n + e+

νe + n→ p + e−

Introduction Core-collapse SN1987A Prospects Conclusions

Simulations

Figure: 1D simulation of supernova (figure 15.7, Giunti)

〈Eνe 〉 ≈ 10 MeV, 〈Eν̄e 〉 ≈ 15 MeV, 〈Eνx 〉 ≈ 20 MeV

Introduction Core-collapse SN1987A Prospects Conclusions

Supernova in February 1987

Sanduleak −69◦ 202 in LargeMagellanic Cloud is progenitor.

type star: blue supergiantdistance: 50.1± 3.1 kpcmass: 20M�

Type II supernova

Neutrinos detected, by

Kamiokande IIIrvine-Michigan-BrookhavenBaksan Scintillator Telescope Figure: SN1987A in 1994

(NASA/ESA Hubble SpaceTelescope)

Introduction Core-collapse SN1987A Prospects Conclusions

Kamiokande II

Cherenkov detector

2000 metric ton of water1000 photomultiplier tubes

Most important reactions

ν̄e + p −→ n + e+

νe + e− −→ νe + e−.

E (e±) ∝ PMT hits.

Figure: Kamiokande II (figure 1, Hirata)

Introduction Core-collapse SN1987A Prospects Conclusions

Measured events

Figure: Hits versus time (figure 4e Hirata 1988)

Set of events at 7:35:35 UT.

Decay of 214Bi causes most eventswith Nhits ≤ 20.

Pµ . 8 · 10−12

Prandom . 10−8

no other special events

Introduction Core-collapse SN1987A Prospects Conclusions

Measured events

Table: The 12 events (table II, Hirata)

Time Energy Angle(s) (MeV) (deg)

0 20.0± 2.9 18± 180.107 13.5± 3.2 40± 270.303 7.5± 2.0 108± 320.324 9.2± 2.7 70± 300.507 12.8± 2.9 135± 230.686 6.3± 1.7 68± 771.541 35.4± 8.0 32± 161.728 21.0± 4.2 30± 181.915 19.8± 3.2 38± 229.219 8.6± 2.7 122± 30

10.433 13.0± 2.6 49± 2612.439 8.9± 1.9 91± 39 Figure: Cross-section (fig. 14bc, Hirata)

Introduction Core-collapse SN1987A Prospects Conclusions

Measured events

Figure: Scatter plot (fig. 13, Hirata)

Introduction Core-collapse SN1987A Prospects Conclusions

Comparison with theory

Delayed explosion 100× more probable than prompt explosion.

Average energy 〈Eν̄e 〉 ≈ 15 MeV.

Neutrinos emitted Nν̄e ≈ 3 · 1057.

Energy emitted E = 3 · 1053 erg.

Time scales

accretion of mass ∆t = 0.7 s,cooling phase ∆t = 4 s

Introduction Core-collapse SN1987A Prospects Conclusions

Neutrino mass

Model independent

Time-of-travel for massive particle depends on energy, this gives

m . E

√E

∆E

∆Tobs

D.

Since D ∼ 50 kpc, E ∼ 15 MeV, ∆E ∼ 15 MeV and ∆Tobs . 12 s,the bound mass is

mνe . 30 eV.

Model dependent

Assuming a delayed supernova model gives

mνe < 5.7 eV (95% CL) .

Introduction Core-collapse SN1987A Prospects Conclusions

Other properties

Several other properties of neutrinos are constrained

Lifetime of electron antineutrino

τν̄e & 1.6 · 105mνe

Eν̄e

yr,

Number of flavours Nν . 6,

Magnetic momentµνe . 10−12µB ,

Charge radius of right-handed neutrinos⟨r2⟩R. 2× 10−33 cm2,

Electric charge of electron neutrino

qνe . 10−17e.

Introduction Core-collapse SN1987A Prospects Conclusions

Detectors able to detect supernova neutrinos

Super-Kamiokande, SNO, LVD, KamLANDExpect 104 neutrinos in galactic supernova

νe mass limit at best 3 eV

νµ and ντ mass limit at best 30 eV.

SuperNova Early Warning System

Introduction Core-collapse SN1987A Prospects Conclusions

Supernovae take place in time scale of ten seconds.

Theory and experiment agree.

Neutrinos crucial to explain supernovae

neutrinos carry away most of the energy released,neutrinos allow to see inside the explosion.

Supernovae important to study neutrinos.

Introduction Core-collapse SN1987A Prospects Conclusions

Further reading

K. S. Hirata et al.Observation in the kamiokande-ii detector of the neutrinoburst from supernova sn1987a.Phys. Rev. D, 38(2):448–458, Jul 1988.

C. Giunti C.W. Kim.Fundamentals of Neutrino Physics and Astrophysics.Oxford University Press, 2007.

K. Zuber.Neutrino Physics.Taylor & Francis, 2003.