Spectrum of the Supernova Relic Neutrino Background

Spectrum of the Supernova Relic Neutrino Background Ken ichiro Nakazato (Tokyo University of Science) Numazu Workshop 2015, Sep. 1, 2015

Outline 1. Introduction Neutrino signal from supernovae Supernova Neutrino Database (K. Nakazato et al. 2013, ApJS 205, 2) 2. Supernova Relic Neutrinos Metallicity evolution of galaxies (K. Nakazato et al. 2015, ApJ 804, 75) 3. Summary

Supernova neutrinos Clue for puzzle in supernova physics. Burrows (1988) SN1987A @ Kamiokande

Light curves and spectra Neutrino emission continues for 10 seconds. (diffusion time scale) x e e Nakazato+ (2013) Fischer+ (2012)

3 phases of neutrino emission 1 2 3 x 1 neutronization burst ~ O (10 ms) e e 2 accretion phase ~ O (100 ms) 3 cooling phase ~ O (10 sec) Nakazato+ (2013)

Neutronization burst Shock dissociates nuclei. Protons capture electrons emitting e. deleptonization Shock :neutron A :proton A :electron A A A e p + e n + :electron

Accretion phase collapse Gravitational potential of accreted matter converts to thermal energy. accretion proto-neutron star shock Neutrinos of all flavors are emitted by thermal process.

Cooling phase Shock revives and propagates to outer layer. Heating by matter accretion stops. proto-neutron star Luminosity and mean energy of neutrinos drop.

When does shock revive? Possibly characterizing explosion mechanism. e.g. convection vs. SASI Whether the transition from accretion phase to cooling phase is early or late? Affecting the features of emitted neutrinos. More neutrinos would be emitted for later transition cases, because matter accretes more.

Supernova neutrino database http://asphwww.ph.noda.tus.ac.jp/snn/

Progenitor models mass: M = 13-50M (4 cases) metallicity: Z = 0.02, 0.004 (2 cases) among total 8 models 7 models: Supernovae 1 model: Black Hole (Failed supernova) 30M, Z = 0.004 The maximum neutron star mass of adopted equation of state

radiation hydrodynamics Spherically symmetric full GR hydrodynamics (Yamada 1997) Metric:Misner & Sharp (1964) Radial mesh:255 non uniform zones accretion + Neutrino transport (Boltzmann solver) phase (Yamada et al. 1999; Sumiyoshi et al. 2005) Species : e e ( ) ( ) Energy mesh : 20 zones (0 300 MeV) Reactions : e - + p n + e, e + + n p + e, + N + N, + e + e, e + A A + e -, + A + A, e - + e + +, * +, N + N N + N + +

Proto-neutron star cooling Multigroup Flux Limited Duffusion scheme (Suzuki 1994) Species : e e ( ) cooling Energy mesh : 20 phase zones (same with rad-hydro.) Reactions : e - + p n + e, e + + n p + e, + N + N, + e + e, e + A A + e -, + A + A, e - + e + +, * +, N + N N + N + + (*) Equation of State by H. Shen is adopted for both computations.

Shock revival time Suggestions from observables. NS mass distribution 100-200 ms explosion energy & 56 Ni yield 300-400 ms We set t rev = 100, 200, 300 ms Belczynski et al. (2012) Yamamoto et al. (2013)

Luminosity and mean energy 13M, Z = 0.02, t revive = 100 ms This work Totani+ (1998) x e e

Neutrino spectra Number luminosity This work Totani+ (1998)

Time integrated spectra They are similar to Fermi-Dirac distribution below 30 MeV. High energy tails are accretion phase origin.

Systematics early shock revival late If the shock revival time is late, the total energy of emitted neutrino gets high.

Spectra for failed supernovae soft hard It is followed until the black hole formation. Total number of emitted neutrinos depends on nuclear equation of state (EOS). Hard EOS produces more neutrinos.

Supernova relic neutrinos The flux of neutrinos and antineutrinos emitted by all corecollapse supernovae in the causallyreachable universe. Is it possible to study something from supernova relic neutrinos? We are here! z = 0 z = 1 z = 2 time

Detection status The upper limit is near theoretical predictions.

Formulation de de 1 z Supernova neutrino spectrum: Cosmological parameters Initial mass function: (Salpeter)

Formulation de de 1 z Core collapse rate: cosmic star formation rate related to stellar mass distribution of galaxies (Drory & Alvarez, 2008) SFR of galaxy stellar mass function

Cosmic star formation rate It has a peak at redshift z ~ 1-2, but uncertainty is large. conversion from UV luminosity to star formation rate of galaxy dust obscuration correction Note: Contribution from stars in z > 2 is small. Cosmic star formation rate [M yr -1 Mpc -3 ] Observation of galaxies Hopkins & Beacom (2006) Drory & Alvarez (2008) Theoretical model Kobayashi et al. (2013)

Formulation de de 1 z Metallicity distribution function of progenitors mass metallicity relation (Maiolino+, 2008) SFR of galaxy stellar mass function (Drory & Alvarez, 2008)

Cosmic chemical evolution Big Bang galaxy formation, evolution Now supernovae H, He only metal increase Old stars are low metallicity. Low metallicity stars have massive cores. Failed supernova progenitors are included.

Fraction of failed supernovae Fraction of failed supernovae M Z 0.02 0.004 13M SN SN 20M SN SN 30M SN BH 50M SN SN Nakazato+ (2015) It increases with redshift because metal poor stars are abundant in high redshift universe.

Spectra of SN relic neutrinos Flux [cm -2 s -1 MeV -1 ] 10 1 0.1 0.01 0.001 difference of SFR 0 10 20 30 40 50 Neutrino Energy [MeV] Event [MeV -1 (22.5kt yr) -1 ] 0.16 0.12 0.08 0.04 0 difference of SFR low high 0 10 20 30 40 50 Positron Energy [MeV] Uncertainty is large in low energy region. Reflecting large uncertainty of cosmic star formation rate in high redshift universe

Spectra of SN relic neutrinos Flux [cm -2 s -1 MeV -1 ] 10 1 0.1 0.01 0.001 difference of t revive 200 ms 100 ms 300 ms 0.12 0.08 0.04 0 10 20 30 40 50 0 10 20 30 40 50 Neutrino Energy [MeV] Positron Energy [MeV] Uncertainty is large in high energy region. If the shock revival is late, proto-neutron star is heated and neutrino spectrum gets hard. Event [MeV -1 (22.5kt yr) -1 ] 0 difference of t revive early late

Flux [cm -2 s -1 MeV -1 ] Spectra of SN relic neutrinos 10 1 0.1 0.01 0.001 difference of EOS Shen 0.12 0.08 difference of EOS LS 0.04 soft (220 MeV) 0 0 10 20 30 40 50 0 10 20 30 40 50 Neutrino Energy [MeV] Positron Energy [MeV] Uncertainty is large in high energy region. If the EOS is hard, the black hole formation is delayed and neutrino spectrum gets hard. Event [MeV -1 (22.5kt yr) -1 ] hard

Uncertainties on SRN spectrum Flux [cm -2 s -1 MeV -1 ] 10 1 0.1 0.01 0.001 cosmic SFR low high 0 10 20 30 40 50 Neutrino Energy [MeV] 0.001 0 10 20 30 40 50 Neutrino Energy [MeV] Uncertainty on SRN spectrum in low energies is mainly from cosmic star formation rate. 10 1 0.1 0.01 from SFR SFR +other uncertainties min. max. To investigate star formation history, low energy is better and SK-Gd is promising.

Summary We have constructed Supernova Neutrino Database, where the predictions for various cases are included. Taking into account the evolutions of stellar mass function and mass metallicity relation of galaxies, flux of supernova relic neutrino is estimated with Supernova Neutrino Database. Since uncertainty on SRN spectrum in low energies is mainly from cosmic star formation rate, low energy is better and SK-Gd is promising to investigate star formation history.