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Outline. Observations of HE neutrinos by IceCube Theoretic models for extragalactic neutrinos Possible component from Galactic center. High energy neutrinos– a new window. MeV neutrinos: detected • Solar & SN1987A neutrinos • Stellar physics (Sun’s core, SNe core collapse)

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Outline

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  1. Outline • Observations of HE neutrinos by IceCube • Theoretic models for extragalactic neutrinos • Possible component from Galactic center

  2. High energy neutrinos– a new window • MeV neutrinos: detected • Solar & SN1987A neutrinos • Stellar physics (Sun’s core, SNe core collapse) • High-energy (>TeV) neutrinos • Study “Cosmic accelerators” Cosmic rays 1) 2)

  3. Cosmic ray spectrum -2.7 Knee -3.1 UHE CRs Ankle

  4. Cosmic rays below the Knee Shock fronts Fermi acceleration when particles gyrate across high B-fields Cas A Supernova Remnant in X-rays John Hughes, Rutgers, NASA

  5. Gamma-ray evidence for CRs in SNRs p0->γ+γ p+p->p+p+ p0 Ackermann et al. 2013, Science

  6. Source of UHECRs ? 1. AGN (Berezinsky..) Acceleration of UHECRs: R_L<R  B*R>E/Zqv Hillas Plot 2. GRB (Waxman, Vietri, …) 3 Galaxy clusters Hypernova …

  7. IceCube

  8. IceCube: diffuse PeV neutrinos detected ! IceCube collaboration , 2013, PRL • 2 events / 672.7 days – atmospheric neutrino background expectation 0.08 events • preliminary p-value: 0.0029 (2.8σ) • PeV neutrino-induced cascade events

  9. 22 November 2013

  10. More TeV-PeV neutrinos • 28 events • significance > 4 σ • atm. Background:

  11. Arriving directions 28 events • isotropic distribution dominantly extragalactic origin • a part of them could come from Galactic sources (Fox,Kashiyama, & Meszaros 2013)

  12. GRB scenario Waxman & Bahcall 1997

  13. The earliest prediction Waxman & Bahcall 97, 99 Shock radius: and Baryon composition Normalized with UHECR flux: ~1 neutrino/100 GRB !

  14. But failed in searching for coincident neutrinos • searched 509 GRBs so far… IceCube 2012 But see He et al. 2012

  15. Diffuse neutrinos from GRBs Liu & Wang 2013 • Untriggered GRBs produce 2 times larger flux • Expected total flux • High-luminosity GRBs are insufficient to account for two PeV neutrinos !

  16. Starburst galaxy scenario Loeb & Waxman 2006 • Normalized with the local 1.4 GHz energy production rate • But, Normal SNRs can only accelerate CR to PeV, while IceCube neutrinos need 50 PeV CRs ? Eν ~ 0.04 Ep: PeV neutrino ⇔ 20-30(1+z) PeV CR proton

  17. ISM Hypernova remnant scenario (Liu, Wang et al. 2014) • Hypernova prototype: SN 1998bw: faster ejecta and greater kinetic energy • Semi-relativistic (v~c, or Γβ≥1) outflow • Hypernovae can accelerate CR protons to 10^18 eV • CR protons collide with the surrounding gas and produce neutrinos (Wang et al. 2007) Proton Hypernova remnant

  18. Nearby hypernova/GRBs SN 1998bw • Radio afterglow modeling of SN1998bw: E>1e49 erg, Γ~1-2 • X-ray afterglow: E~5e49 erg, \beta=0.8 (Waxman 2004) Mildly relativistic ejecta component with energy >1e50 erg

  19. ISM Neutrino production efficiency (Liu, Wang et al. 2014) Proton • pp efficiency • Two escape ways: 1) diffusion 2) advection • pp efficiency in star-forming galaxies & starburst galaxies

  20. Neutrino spectrum from HNe (Liu, Wang et al. 2014) • SBG: star-burst galaxies • NSF: normal star-forming galaxies S=-2.2-2.3

  21. Detailed calculation Chang, Liu & Wang 2015 • Use infrared luminosity function obtained by Herschel PEP/HerMES (Gruppioni et al. 2013) • Sum up contributions by different galaxy populations • The flux and spectrum can match the observations • Star-forming galaxies also contribute significantly to the diffuse gamma-ray background

  22. Tidal disruption event scenario ? • UHECR acceleration in TDE jets (Farrar & Piran 2014) • CR energetics

  23. TDE neutrinos

  24. Sufficient diffuse flux ? To explain the IceCube neutrino flux, one need f_pγ≈1 Could contribute a significant fraction !

  25. Fermi bubble neutrinos ?

  26. Fermi bubble neutrinos ? Lunardini & Razzaque 2012

  27. Galactic hypernova remnants (Fox et al. 2013) • A small fraction of PeV sources close to the Galactic center might be the Galactic unidentified sources - which in turn could be HNe; • Lack of radio or X-ray counterparts—hadronic interactions • BUT: only 1-3 neutrinos

  28. Summary • Starbursts, Hypernova remnants, TDE are candidate sources of HE neutrinos • Galactic center may contribute a subdominant component • IceCube PeV neutrinos could come from the same sources of UHECRs

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