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Testing the origin of the UHECRs with neutrinos

Testing the origin of the UHECRs with neutrinos. Walter Winter DESY, Zeuthen, Germany Kavli Institute for Theoretical Physics (KITP), Santa Barbara, CA, USA UHECR 2014,Springdale, UT, USA Oct. 12-15, 2014. TexPoint fonts used in EMF: A A A. Contents. Introduction

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Testing the origin of the UHECRs with neutrinos

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  1. Testing the origin of the UHECRs with neutrinos Walter Winter DESY, Zeuthen, GermanyKavli Institute for Theoretical Physics (KITP), Santa Barbara, CA, USA UHECR 2014,Springdale, UT, USAOct. 12-15, 2014 TexPoint fonts used in EMF: AAA

  2. Contents • Introduction • Can the observed neutrinos come from the same sources as the UHECRs? • GRBs as test case for the UHECR-neutrino connection • Summary

  3. Cosmic messengers Physics of astrophysical neutrino sources = physics ofcosmic ray sources

  4. 2014: 37 neutrinos in the TeV-PeV range Physics World Breakthrough of the year 2013 Where do these come from? Prompt atmospherics?Directional information: Clustering?Isotropic/from Galactic plane/Galactic center?Why no events > few PeV?Can these come from the sources of the ultra-highenergy cosmic rays? Which source class? More than one? Flavor composition?  Requires more statistics Science 342 (2013) 1242856; update by Gary Hill @ Neutrino 2014

  5. Connection with primary nuclei? • In pp and pg interactions, the secondary pions take about 20% of the proton energy, the neutrinos about 5% (per flavor) • PeV neutrinos must come from 20-500 PeV nuclei (depending on comp.) • Observed cosmic ray composition non-trivial function of energy (at Earth!) • Simple example: Neutrinos fromcosmic rayinteractions with hydrogenin the Milky Way[O(0.1-1) event] • Connection with UHECR sources requires extrapolation over several orders of magnitude both in spectrum and composition Joshi, Winter, Gupta, MNRAS, 2014 nprima-ries UHECRs Gaisser, Stanev, Tilav, 2013

  6. Fitting the observed neutrino spectrum • Simplest possible model: Ap (or AA) interactions in sources;SFR evolution • Possible fits to data: Protons a=2 B ~ 104 G(magnetic field effects on sec. pions, muons, kaons) Protons, a=2.5[Problem: Fermi diffuse g-ray bound Murase, Ahlers, Lacki, PRD 2013] Nuclei a=2, Emax=1010.1 GeVComposition at sourcewith b=0.4 Protonsa=2Emax=107.5 GeV WW, arXiv:1407.7536(PRD, accepted)

  7. Connection to UHECRs? • Yes, but: Energy input per decade very different in neutrino-relevant and UHECR energy ranges(Energetics seem to favor a~2, see e.g. B. Katz, E. Waxman, T. Thompson, and A. Loeb (2013), 1311.0287)  will come up again later! Yes, but: Synchrotron losses limit maximal proton energies as well. Need large Doppler factors (e. g. GRBs) Protons, a=2.5[Problem: Fermi diffuse g-ray bound Murase, Ahlers, Lacki, PRD 2013] Protons a=2 B ~ 104 G Nuclei a=2, Emax=1010.1 GeVComposition at sourcewith b=0.4 Protonsa=2Emax=107.5 GeV Yes, but: Need energy-dependent escape timescale leading to break/cutoff within source (diff. from ejection!)see e.g. Liu et al, PRD, 2004; arXiv:1310.1263 Yes, but: A(E) change somewhat too shallow to match observation; difference source-observation from propagation? WW, arXiv:1407.7536(PRD, accepted)

  8. GRBs as a test case • Idea: Use timing and directional information to suppress atm. BGs • Stacking limit exceeds observed neutrino flux (~10-8) by one order of magnitude; interesting to test specific modelsNature 484 (2012) 351 • Prediction (One zone model.based on fixed collision radius models) almost reached(some recent corrections!) (Source: NASA) Coincidence! Neutrino observations(e.g. IceCube, …) (Source: IceCube) GRB gamma-ray observations(e.g. Fermi, Swift, etc) (Hümmer, Baerwald, Winter, PRL 108 (2012) 231101; method based on Guetta et al, 2004; Waxman, Bahcall 1997)

  9. GRB - Internal shock model (Source: SWIFT) G ~ 200-1000 Engine(intermittent) “Isotropic equivalentenergy“ Prompt phaseCollision of shells Shocks Particle acc. Observable:Light curves (Simulation by M. Bustamante)

  10. UHECR-neutrino connection: escape mechanisms?Baerwald, Bustamante, Winter, Astrophys. J. 768 (2013) 186 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

  11. An example (before propagation) (only adiabatic energy losses) • For high enough acceleration efficiencies:R‘L can reach shell thickness at highest energies(if E‘p,max determined by t‘dyn) • Hard spectrum, aka “high pass filter“ (Globus et al, 2014) • Relative importance depends on optical thickness to pg interactions(from: Baerwald, Bustamante, Winter, Astrophys. J. 768 (2013) 186) Neutron spectrumharder than E-2proton spectrum

  12. Combined source-propagation model: Ankle transition (ap=2, fit range 1010 ... 1012 GeV) • Neutron-dominated cases can be constrained by neutrino emission • Baryonic loading fe-1 (energy protons to photons) typically somewhat larger than IceCube assume, to fit UHECR data (here Liso=1052 erg s-1, Eiso=3 1052 erg) G=300 G=800 (Baerwald, Bustamante, Winter, Astropart. Phys. 62 (2015) 66; figures with TA data)

  13. Combined source-propagation model: Dip transition (ap=2.5 with SFR evolution, fit range 109 ... 1012 GeV) • Neutron-dominated cases even more extreme • Required baryonic loading fe-1 extremely large; implication of unequal energy output per decade (bolometric correction) G=300 G=600 1050.5 erg/s (Baerwald, Bustamante, Winter, Astropart. Phys. 62 (2015) 66; figures with TA data)

  14. Parameter space constraints (ankle model, fit to TA data) Example: Moderate acc. efficiency, escape by Bohm-like diffusion, SFR evolution of sources,ankle transition log10 fe-1(baryonic loading) obtained from fit Direct escape Optically thick pg IceCube expectation (15yr) Best-fit (shaded contours: TA UHECR fit) Current IceCube limit (Baerwald, Bustamante, Winter, Astropart. Phys. 62 (2015) 66; figures with TA data) … but - maybe - assigning one parameter set to all shells is too simple?

  15. The future: more dynamical collision models • Set out a number of shells with a Lorentz factor distribution • Shells collide, merge and cool by radiation of energy • Light curve predictable (see below) • Efficient energy dissipation (e. g. into gamma-rays) requires broad Lorentz factor distribution (Bustamante, Baerwald, Murase, Winter, 2014; based on collision model Kobayashi, Piran, Sari, 1997; see Globus et al, 2014 for a similar approach)

  16. Consequences for different messengers • Collision radii reach from below photosphere to circumburst medium • UHECR escape as neutrons (red) and directly (blue) at intermediate radii • Energy output ~ no of collsions x energy per collision (counting important!) • The burst looks different in different messengers! (Bustamante, Baerwald, Murase, Winter, 2014)

  17. Consequences for neutrino production Eiso=1053 erg per GRB • Neutrino flux comes from a few collisions at photosphere • Photospheric radius and photohadronic interactions both depend on particle densities (scale at same way) • Super-photospheric (minimal?) prediction hardly depends on baryonic loading, G(different from earlier works!) • Testable in high-energy extension of IceCube? • Sub-photospheric contribution could be much larger. However: photons from below photosphere not observable (Bustamante, Baerwald, Murase, Winter, 2014)

  18. Summary • Neutrino observations open new window to cosmic ray source identification; data (discovery and constraints) become meaningful • UHECR connection somewhat more challenging, as several orders of magnitude in energy between UHECRs and primaries leading to observed neutrino flux • GRBs are an interesting test case, as • The constraints are strongest on GRBs because of timing cuts • Well-motivated models for gamma-ray emission exist • IceCube data already test the parameter space • Different messengers are produced in different regions of a GRB. Multi-messenger connections are more model-dependent than previously anticipated • Heavy nuclei are anticipated to escape from larger radii than protons, as disintegration is to be avoided – but they can survive

  19. BACKUP

  20. Neutrino production Q(E) [GeV-1 cm-3 s-1] per time frameN(E) [GeV-1 cm-3] steady spectrum Dashed arrows: kinetic equations include cooling and escape Input  Object-dependent: B‘ Opticallythinto neutrons from: Baerwald, Hümmer, Winter,Astropart. Phys. 35 (2012) 508

  21. Kinetic equations (steady state, one zone) • Energy losses in continuous limit:b(E)=-E t-1lossQ(E,t) [GeV-1 cm-3 s-1] injection per time frame (from sep. acc. zone)N(E,t) [GeV-1 cm-3] particle spectrum including spectral effectsNB: Need N(E) to compute particle interactions • Simple case: No energy losses b=0: • Special cases: • tesc ~ R/c (leaky box) • tesc ~ E-a . Consequence: N(E) ~ Qinj(E) E-a, Escape: Qesc(E) = N(E)/tesc~ Qinj(Neutrino spectrum from N(E) can have a break which is not present in escaping primaries Qesc(E)) Injection Energy losses Escape

  22. 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 • Decouples maximal neutrino and proton energies nm Pile-up effect Flavor ratio! Spectralsplit E‘c E‘c E‘c Adiabatic Baerwald, Hümmer, Winter,Astropart. Phys. 35 (2012) 508; also: Kashti, Waxman, 2005; Lipari et al, 2007

  23. From the source to the detector: UHECR transport • Kinetic equation for co-moving number density: • Energy losses UHECR must fromfrom our local environment (~ 1 Gpc at 1010 GeV, ~ 50 Mpc at 1011 GeV) Expansion ofUniverse Pair productionBlumenthal, 1970 PhotohadronicsHümmer, Rüger, Spanier, Winter, 2010 CR inj.z-dep! [here b=-dE/dt=E t-1loss] GZK cutoff (M. Bustamante)

  24. Cosmogenic neutrinos • Prediction depends on maximal proton energy, spectral index g, source evolution, composition • Can test UHECR beyond the local environment • Can test UHECR injection independent of CR production model  constraints on UHECR escape Cosmogenic neutrinos EeV Protons (courtesy M. Bustamante; see also Kotera, Allard, Olinto, JCAP 1010 (2010) 013)

  25. Transition between Galactic (?) and extragalactic cosmic rays at different energies: Ankle model: Injection index g ~ 2 possible ( Fermi shock acc.) Transition at > 4 EeV Dip model: Injection index g ~ 2.5-2.7 (how?) Transition at ~ 1 EeV Characteristic shape by pair production dip UHECR transition models Extra-galactic Figure courtesy M. Bustamante; for a recent review, see Berezinsky, arXiv:1307.4043

  26. Redshift distribution Can be integrated over.Total number of bursts in the observable universe Can be directly determined (counted)! Order 1000 yr-1 More details: Gamma-ray observables? ~ (1+z)a SFR Threshold correction (Kistler et al, Astrophys.J. 705 (2009) L104)

  27. Consequence: Local GRB rate • The local GRB rate can be written aswhere fz is a cosmological correction factor: (for 1000 observable GRBs per year and 30% of all bursts seen) (Baerwald, Bustamante, Winter, arXiv:1401.1820)

  28. Required baryonic loading (analytical) • Required energy ejected in UHECR per burst: • In terms of g-ray energy: • Baryonic loading fe-1~50-100 for E-2 inj. spectrum (fbol ~ 0.2), Eg,iso ~ 1053 erg, neutron model (fCR ~ 0.4)[IceCube standard assumption: fe-1~10] ~1.5 to fit UHECR observations ~5-25 Fraction of energyin CR production? How much energyin UHECR? Energy in protons vs. electrons (IceCube def.)

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