Introduction Core-collapse SN1987A Prospects Conclusions. Supernova neutrinos. Ane Anema. November 12, 2010

Transcription

1 Supernova neutrinos Ane Anema November 12, 2010

2 Outline 1 Introduction 2 Core-collapse 3 SN1987A 4 Prospects 5 Conclusions

3 Types of supernovae Figure: Classification (figure 15.1, Giunti)

4 Supernova rates Figure: Rates (figure 15.2, Giunti) Upper bound on supernovae in Milky Way 13 supernovae per century 90% CL.

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

6 Interior structure of massive star Table: Burning phases for 15M star (table 15.2, Giunti) Phase Time scale (yr) H He C Ne O 2.58 Si Figure: Interior structure (figure 15.6, Giunti)

7 Collapse Iron core M c 1.26 M, R c 10 3 km, p c g cm 3, T c 1 MeV. 1 The iron core contracts. 2 Temperature of core increases, so 3 Electron capture γ + 56 Fe 13α + 4n 124 MeV. e + N (Z, A) N (Z 1, A) + ν e e + p n + ν e 4 Number of electrons in core decreases. Neutrinos are emitted.

8 Collapse Chandrasekhar limit The electron gas pressure must counteract gravity. M 5.83Y 2 e M where Y e = N p N p + N n 5 Fewer electrons implies lower Chandrasekhar limit. 6 Iron core collapses under gravitational pressure. 7 Photodissociation and electron capture rates increase. E ν MeV, L erg s L, E erg 10 3 M. 8 Neutrinos get trapped in inner core (10 11 g cm 3 ). 9 Nucleon gas halts collapse of inner core (10 14 g cm 3, t 1s).

9 Proto-neutron star Proto-neutron star Inner core has density g cm 3, radius 10 km. Outer core has density 10 9 g cm 3, radius 100 km.

10 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 (10 11 g cm 3 ). Release of neutrinos L erg s L, E erg 10 3 M, time scale: a few milliseconds. 14 Shock wave weakens by photodissociation.

11 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 erg of gravitational energy released.

12 Cooling phase Core of proto-neutron star has temperature of 40 MeV. Pair annihilation e + e + ν + ν Bremsstrahlung e ± + N e ± + N + ν + ν N + N N + N + ν + ν Plasmon decay γ ν + ν Photoannihilation γ + e ± e ± + ν + ν

13 Neutrinosphere Inner region of proto-neutron star is opaque to neutrinos. Neutrinosphere is outer region of proto-neutron star not opaque to neutrinos. Neutrinosphere depends on flavour and energy of neutrino. both ν e and ν e interact via charged and neutral current, other neutrinos only via neutral current. Radius of neutrinosphere about km. Opacities for ν e, ν e different due to few protons in outer core ν e + p n + e + ν e + n p + e

14 Simulations Figure: 1D simulation of supernova (figure 15.7, Giunti) E νe 10 MeV, E νe 15 MeV, E νx 20 MeV

15 Supernova in February 1987 Sanduleak in Large Magellanic Cloud is progenitor. type star: blue supergiant distance: 50.1 ± 3.1 kpc mass: 20M Type II supernova Neutrinos detected, by Kamiokande II Irvine-Michigan-Brookhaven Baksan Scintillator Telescope Figure: SN1987A in 1994 (NASA/ESA Hubble Space Telescope)

16 Kamiokande II Cherenkov detector 2000 metric ton of water 1000 photomultiplier tubes Most important reactions ν e + p n + e + ν e + e ν e + e. E (e ± ) PMT hits. Figure: Kamiokande II (figure 1, Hirata)

17 Measured events Figure: Hits versus time (figure 4e Hirata 1988) Set of events at 7:35:35 UT. Decay of 214 Bi causes most events with N hits 20. P µ P random 10 8 no other special events

18 Measured events Table: The 12 events (table II, Hirata) Time Energy Angle (s) (MeV) (deg) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 39 Figure: Cross-section (fig. 14bc, Hirata)

19 Measured events Figure: Scatter plot (fig. 13, Hirata)

20 Comparison with theory Delayed explosion 100 more probable than prompt explosion. Average energy E νe 15 MeV. Neutrinos emitted N νe Energy emitted E = erg. Time scales accretion of mass t = 0.7 s, cooling phase t = 4 s

21 Neutrino mass Model independent Time-of-travel for massive particle depends on energy, this gives E T obs m E E D. Since D 50 kpc, E 15 MeV, E 15 MeV and T obs 12 s, the bound mass is m νe 30 ev. Model dependent Assuming a delayed supernova model gives m νe < 5.7 ev (95% CL).

22 Other properties Several other properties of neutrinos are constrained Lifetime of electron antineutrino τ νe m ν e E νe yr, Number of flavours N ν 6, Magnetic moment µ νe µ B, Charge radius of right-handed neutrinos r 2 R cm 2, Electric charge of electron neutrino q νe e.

23 Detectors able to detect supernova neutrinos Super-Kamiokande, SNO, LVD, KamLAND Expect 10 4 neutrinos in galactic supernova ν e mass limit at best 3 ev ν µ and ν τ mass limit at best 30 ev. SuperNova Early Warning System

24 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.

25 Further reading K. S. Hirata et al. Observation in the kamiokande-ii detector of the neutrino burst from supernova sn1987a. Phys. Rev. D, 38(2): , Jul C. Giunti C.W. Kim. Fundamentals of Neutrino Physics and Astrophysics. Oxford University Press, K. Zuber. Neutrino Physics. Taylor & Francis, 2003.