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Testing the origin of the UHECRs with neutrinos

Investigating the potential connection between Ultra-High Energy Cosmic Rays (UHECRs) and neutrinos, exploring GRBs as test cases, composition and sources of TeV-PeV range neutrinos, and connections to UHECR sources. Detailed analysis based on astrophysical models and data.

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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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