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.