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Neutrinos from gamma-ray bursts, and tests of the cosmic ray paradigm

Neutrinos from gamma-ray bursts, and tests of the cosmic ray paradigm. TeVPA 2012 TIFR Mumbai, India Dec 10-14, 2012 Walter Winter Universität Würzburg. TexPoint fonts used in EMF: A A A A A A A A. Contents. Introduction Simulation of sources Multi-messenger physics with GRBs

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Neutrinos from gamma-ray bursts, and tests of the cosmic ray paradigm

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  1. Neutrinos from gamma-ray bursts, and tests of the cosmic ray paradigm TeVPA 2012TIFR Mumbai, India Dec 10-14, 2012Walter Winter Universität Würzburg TexPoint fonts used in EMF: AAAAAAAA

  2. Contents • Introduction • Simulation of sources • Multi-messenger physics with GRBs • Gamma-rays versus neutrinos • Neutrinos versus cosmic rays • Role of new physics? • Summary and conclusions

  3. The two paradigms for extragalactic sources:AGNs and GRBs • Active Galactic Nuclei (AGN blazars) • Relativistic jets ejected from central engine (black hole?) • Continuous emission, with time-variability • Gamma-Ray Bursts (GRBs): transients • Relativistically expanding fireball/jet • Neutrino production e. g. in prompt phase(Waxman, Bahcall, 1997) Nature 484 (2012) 351

  4. Cosmic ray source(illustrative proton-only scenario, pg interactions) If neutrons can escape:Source of cosmic rays Neutrinos produced inratio (ne:nm:nt)=(1:2:0) Delta resonance approximation: Cosmic messengers (ne:nm:nt)=(1:1:1)after flavor mixing One nmper cosmic ray High energetic gamma-rays;typically cascade down to lower E

  5. “Minimal“ (top down) n model Q(E) [GeV-1 cm-3 s-1] per time frameN(E) [GeV-1 cm-3] steady spectrum Dashed arrows: include cooling and decay Input: B‘ Addl.prod.processes Opticallythinto neutrons from: Baerwald, Hümmer, Winter,Astropart. Phys. 35 (2012) 508

  6. Peculiarity for neutrinos: Secondary cooling Example: GRB Decay/cooling: charged m, p, K • Secondary spectra (m, p, K) loss-steepend above critical energy • E‘c depends on particle physics only (m, t0), and B‘ • Leads to characteristic flavor composition and shape • Very robust prediction for sources? [e.g. any additional radiation processes mainly affecting the primaries will not affect the flavor composition] • A way to directly measure B‘? nm Pile-up effect Spectralsplit E‘c E‘c E‘c Adiabatic Baerwald, Hümmer, Winter,Astropart. Phys. 35 (2012) 508; also: Kashti, Waxman, 2005; Lipari et al, 2007

  7. The “magic“ triangle Properties of neutrinos reallyunterstood? g Satellite experiments(burst-by-burst) ?(energy budget, ensemble fluctuations, …) e.g. Eichler, Guetta, Pohl, ApJ 722 (2010) 543; Waxman, arXiv:1010.5007; Ahlers, Anchordoqui, Taylor, 2012 … Partly common fudgefactors: how many GRBsare actually observable?Baryonic loading?Dark GRBs? … Model-dependent predictionWaxman, Bahcall, PRL 78 (1997) 2292; Guetta et al., Astropart. Phys. 20 (2004) 429 GRB stacking Robust connectionif CRs only escape as neutrons produced in pg interactions Ahlers, Gonzalez-Garcia, Halzen, Astropart. Phys. 35 (2011) 87 CR n Neutrino telescopes (burst-by-burst or diffuse) CR experiments (diffuse)

  8. g GRB stacking n (Source: IceCube) • Idea: Use multi-messenger approach • Predict neutrino flux fromobserved photon fluxesevent by event (Source: NASA) Coincidence! Neutrino observations(e.g. IceCube, …) GRB gamma-ray observations(e.g. Fermi, Swift, etc) Observed:broken power law(Band function) (Example: IceCube, arXiv:1101.1448) E-2 injection

  9. Gamma-ray burst fireball model:IC-40+59 data meet generic bounds • Generic flux based on the assumption that GRBs are the sources of (highest energetic) cosmic rays(Waxman, Bahcall, 1999; Waxman, 2003; spec. bursts:Guetta et al, 2003) Nature 484 (2012) 351 IC-40+59 stacking limit • Does IceCube really rule out the paradigm that GRBs are the sources of the ultra-high energy cosmic rays?

  10. Revision of neutrino flux predictions Analytical recomputationof IceCube method (CFB): cfp: corrections to pion production efficiency cS: secondary cooling and energy-dependenceof proton mean free path(see also Li, 2012, PRD) G ~ 1000 G ~ 200 Comparison with numerics: WB D-approx: simplified pg Full pg: all interactions, K, …[adiabatic cooling included] (Baerwald, Hümmer, Winter, Phys. Rev. D83 (2011) 067303;Astropart. Phys. 35 (2012) 508; PRL, arXiv:1112.1076)

  11. Systematics in aggregated fluxes • z ~ 1 “typical“ redshift of a GRB • Neutrino flux overestimated if z ~ 2 assumed(dep. on method) • Peak contribution in a region of low statistics • Ensemble fluctuations of quasi-diffuse flux Weight function:contr. to total flux Distribution of GRBsfollowing star form. rate (strongevolutioncase) 10000 bursts (Baerwald, Hümmer, Winter, Astropart. Phys. 35 (2012) 508)

  12. Quasi-diffuse prediction • Numerical fireball model cannot be ruled out yet with IC40+59 for same parameters, bursts, assumptions • Peak at higher energy![at 2 PeV, where two cascade events have been seen] “Astrophysical uncertainties“:tv: 0.001s … 0.1sG: 200 …500a: 1.8 … 2.2ee/eB: 0.1 … 10 (Hümmer, Baerwald, Winter, Phys. Rev. Lett. 108 (2012) 231101)

  13. Model dependence • Not only normalization, but also uncertainties depend on assumptions: Internal shock model,target photons from synchrotron emission/inverse Compton from Fig. 3 of IceCube,Nature 484 (2012) 351; uncertainties from Guetta, Spada, Waxman, Astrophys. J. 559 (2001) 2001 Internal shock model,target photons from observation, origin not specified from Fig. 3 of Hümmer et al, PRL 108 (2012) 231101 Model dependence Dissipation radius not specified (e. g. magnetic reconnection models), target photons from observation, origin not specified from Fig. 3 of He et al, ApJ. 752 (2012) 29 (figure courtesy of Philipp Baerwald)

  14. Neutrinos-cosmic rays n CR • If charged p and n produced together: • GRB not exclusive sources of UHECR? CR leakage? Ensemble fluctuations? (Ahlers, Anchordoqui, Taylor, 2012) Consequences for (diffuse) neutrino fluxes Fit to UHECR spectrum Ahlers, Gonzalez-Garcia, Halzen, Astropart. Phys. 35 (2011) 87

  15. CR escape mechanisms(Baerwald, Spector, Bustamante, Waxman, Winter, to appear) Optically thin(to neutron escape) Optically thick(to neutron escape) Direct proton escape(UHECR leakage) • One neutrino per cosmic ray • Protons magnetically confined n n p n n p n n p p n p n p n p n n n n n p n p n n l‘ ~ c t‘pg l‘ ~ R‘L • Neutron escape limited to edge of shells • Neutrino prod. relatively enhanced • pg interaction rate relatively low • Protons leaking from edges dominate

  16. A typical (?) example PRELIMINARY • For high acceleration efficiencies:R‘L can reach shell thickness at highest energies(if E‘p,max determined by t‘dyn) • UHECR from optically thin GRBs can be direct escape-dominated (Baerwald, Spector, Bustamante, Waxman, Winter, to appear) Spectral breakin CR spectrum two componentmodels Neutron spectrumharder than E-2proton spectrum

  17. Parameter space? • The challenge: need high enough Ep to describe observed UHECR spectrum • The acceleration efficiency h has to be high • In tension with the “one neutrino per cosmic ray“ paradigm(Baerwald, Spector, Bustamante, Waxman, Winter, to appear) (tgg=1 for 30 MeV photons) Typicalfor Fermi-LATobserved phase! PRELIMINARY

  18. What if: Neutrinos decay? Decay hypothesis: n2 and n3 decay with lifetimes compatible with SN 1987A bound • Reliable conclusions from flux bounds require cascade (ne) measurements! Point source, GRB, etc analyses needed! • Mechanism to describe why only cascades observed Limits? IceCube events from GRBs? Baerwald, Bustamante, Winter, JCAP 10 (2012) 20; see also Atri‘s talk

  19. Summary Are GRBs the sources of the UHECR? • Gamma-rays versus neutrinos • Revised model calculations release pressure on fireball model calculations • Baryonic loading will be finally constrained (at least in “conventional“ internal shock models) • Neutrinos versus cosmic rays:Cosmic ray escape as neutrons under tension • Cosmic ray leakage must be important • From theory: cosmic ray leakage is a consequence of high accelerationefficiencies, which are needed describe UHECR observations • Gamma-rays vs. neutrinos vs. cosmic rays (in progress) • Reliable conclusions from neutrino limits in presence of neutrino decay must come from cascade measurements g n CR

  20. BACKUP

  21. Consequences for IC-40 analysis • Diffuse limit illustrates interplay with detector response • Shape of prediction used to compute sensitivity limit • Peaks at higher energies IceCube @ n2012:observed two events~ PeV energies from GRBs? (Hümmer, Baerwald, Winter, Phys. Rev. Lett. 108 (2012) 231101)

  22. IceCube method …normalization • Connection g-rays – neutrinos • Optical thickness to pg interactions:[in principle, lpg ~ 1/(ngs); need estimates for ng, which contains the size of the acceleration region] ½ (charged pions) x¼ (energy per lepton) Energy in protons Energy in neutrinos Fraction of p energyconverted into pions fp Energy in electrons/photons (Description in arXiv:0907.2227; see also Guetta et al, astro-ph/0302524; Waxman, Bahcall, astro-ph/9701231)

  23. IceCube method … spectral shape • Example: 3-ag 3-bg 3-ag+2 First break frombreak in photon spectrum(here: E-1 E-2 in photons) Second break frompion cooling (simplified)

  24. Maximal proton energy(in co-moving frame) h=1 h=0.1 PRELIMINARY Baerwald, Spector, Bustamante, Waxman, Winter, to appear

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