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Cosmic Ray Propagation and Galactic Gamma Rays

This study explores the propagation of cosmic rays in the Milky Way galaxy and their interactions with the interstellar medium, focusing on the evidence of particle acceleration and the dominant feature of diffuse gamma-ray emission. Various astrophysical observations and nuclear and particle physics experiments are combined to build a correct model for studying cosmic ray propagation.

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Cosmic Ray Propagation and Galactic Gamma Rays

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  1. Propagation of Cosmic Rays and Diffuse Galactic Gamma Rays(nuclear physics in cosmic ray studies) Igor V. Moskalenko NASA Goddard Space Flight Center moskalenko@gsfc.nasa.gov with Andy W. Strong(MPE, Germany) &Stepan G. Mashnik(LANL)

  2. All Particle CR Spectrum Synchrotron radiation of ultra-relativistic electrons: evidence of particle acceleration, but not protons… Energetically SNR – most probable sources of CR: ~5x1049 erg per SN (1/30 yr-1) – 5% of the kinetic energy of the ejecta. CR propagate in the Galaxy for some 10 Myr before escape.

  3. EGRET Sky: “GeV Excess” Hunter et al. 1997 Excess The diffuse γ-ray emission is the dominant feature of the γ-ray sky – an evidence of CR interactions in the interstellar medium: bremsstrahlung, IC, π0

  4. Reacceleration Model: Secondary Pbars B/C ratio Antiproton flux Ek, GeV Ek, GeV/nucleon

  5. Positron Excess ? HEAT (Coutu et al. 1999) • Are all the excesses connected somehow ? • A signature of a new physics (DM) ? Caveats: • Systematic errors ? • A local source of primary positrons ? • Large E-losses -> local spectrum… e+/e GALPROP Leaky-Box 1 10 100 E, GeV

  6. Propagation of Cosmic Rays: Why? Modeling of the CR propagation and diffuse gamma-ray emission requires to combine many different kinds of data obtained from astrophysical observations, and nuclear and particle physics experiments. Why Do We Need to Study CR Propagation ? In return, a correct model provides a basis for many studies in Astrophysics, Particle Physics, and Cosmology

  7. Dark Matter Signatures in CR Well... But where is the nuclear physics?! Diffuse gammas Antiprotons E, GeV Ek, GeV

  8. Halo Gas, sources CR Propagation: Milky Way Galaxy 1 kpc~3x1018 cm Optical image: Cheng et al. 1992, Brinkman et al. 1993 Radio contours: Condon et al. 1998 AJ 115, 1693 100 pc NGC891 40 kpc 0.1-0.01/ccm 1-100/ccm Sun 4-12 kpc Intergalactic space R Band image of NGC891 1.4 GHz continuum (NVSS), 1,2,…64 mJy/ beam

  9. CR Interactions in the Interstellar Medium Sources: SNRs, Shocks, Superbubbles B Particle acceleration Photon emission ISRF e e gas gas _ + + + - - - P ISM X,γ synchrotron Chandra IC P He CNO diffusion energy losses reacceleration convection etc. bremss π 0 GLAST π LiBeB p Halo He CNO disk solar modulation ACE escape AMS BESS

  10. Heliosphere Flux 20 GeV/n

  11. Transport Equation ψ(r,p,t) – density per total momentum sources (SNR, nuclear reactions…) diffusion convection diffusive reacceleration convection E-loss radioactive decay fragmentation

  12. Volatility Elemental Abundances: CR vs. Solar System CR abundances: ACE O Si Na Fe S CNO Al Cl CrMn LiBeB F ScTiV Solar system abundances

  13. Dark Matter (p,đ,e+,γ) - Nuclear component in CR: What we can learn? Nucleo- synthesis: supernovae, early universe, Big Bang… Stable secondaries: Li, Be, B, Sc, Ti, V Propagation parameters: Diffusion coeff., halo size, Alfvén speed, convection velosity… Radio (t1/2~1 Myr): 10Be, 26Al, 36Cl, 54Mn K-capture: 37Ar,49V, 51Cr, 55Fe, 57Co Energy markers: Reacceleration, solar modulation Extragalactic diffuse γ-rays: blazars, relic neutralino Short t1/2 radio 14C & heavy Z>30 Local medium: Local Bubble Solar modulation Heavy Z>30: Cu, Zn, Ga, Ge, Rb Material & acceleration sites, nucleosynthesis (r-vs. s-processes)

  14. Fixing Propagation Parameters: Standard Way • Using secondary/primary nuclei ratio: • Diffusion coefficient and its index • Propagation mode and its parameters (e.g., reacceleration VA, convection Vz) B/C Interstellar Be10/Be9 Ek, MeV/nucleon Radioactive isotopes: Galactic halo size Zh Zh increase Ek, MeV/nucleon

  15. 51Cr attachment 51V/51Cr Time scale (years) stripping EC decay 51V/51Cr Jones et al. 2001 Ek, MeV/nucleon Ek, MeV/nucleon Niebur et al. 2003 Ek, MeV/nucleon K-capture isotopes Electron attachment & stripping 51V/51Cr ≡ daughter/parent K-capture & reacceleration Solar modulation effect ISM

  16. First Ionization Potential (FIP) vs. Volatility • Low-FIP ~ Refractories • Rb, Cs – break the rule • Other important elements: Na, Cu, Zn, Ga, Ge, Pb Rb Na Cu K Se Ga Cs Ge Zn Pb ~104 K

  17. natSi+p26Al ST W 27Al+p26Al W ST Effect of Cross Sections: Radioactive Secondaries Different size from different ratios… • Errors in CR measurements (HE & LE) • Errors in production cross sections • Errors in the lifetime estimates • Different origin of elements (Local Bubble ?) T1/2=? Zhalo,kpc Ek, MeV/nucleon

  18. Bigger picture…

  19. Matter, Dark Matter, Dark Energy… Ω≡ρ/ρcrit Ωtot =1.02 +/−0.02 ΩMatter =4.4% +/−0.4% ΩDM =23% +/−4% ΩVacuum =73% +/−4% SUSY DM candidate has also other reasons to exist -particle physics… Supersymmetry is a mathematically beautiful theory, and would give rise to a very predictive scenario, if it is not broken in an unknown way which unfortunately introduces a large number of unknown parameters… Lars Bergström (2000)

  20. Example “Global Fit:” diffuse γ’s, pbars, positrons GALPROP/W. de Boer et al. hep-ph/0309029 • Look at the combined (pbar,e+,γ) data • Possibility of a successful “global fit” can not be excluded -non-trivial ! • If successful, it may provide a strong evidence for the SUSY DM Supersymmetry: • MSSM • Lightest neutralino χ0 • mχ ≈ 100-500 GeV • S=½ Majorana particles • χ0χ0−> p, pbar, e+, e−, γ γ pbars e+

  21. CR Fluctuations/SNR stochastic events GeV electrons 100 TeV electrons GALPROP/Credit S.Swordy Electron energy losses Historical variations of CR intensity over 150 000 yr (Be10 in South Polar ice) Bremsstrahlung E(dE/dt)-1,yr Ionization Coulomb IC, synchrotron 107 yr 1 GeV 1 TeV 106 yr Konstantinov et al. 1990 Ekin, GeV

  22. GeV excess: Optimized model antiprotons Uses all sky and antiprotons & gammas to fix the nucleon and electron spectra • Uses antiprotons to fix the intensity of CR nucleons @ HE • Uses gammas to adjust • the nucleon spectrum at LE • the intensity of the CR electrons (uses also synchrotron index) • Uses EGRET data up to 100 GeV Ek, GeV protons electrons x4 x1.8 Ek, GeV Ek, GeV

  23. Longitude Profiles |b|<5° 50-70 MeV 0.5-1 GeV 2-4 GeV 4-10 GeV

  24. Extragalactic Gamma-Ray Background Predicted vs. observed E2xF Sreekumar et al. 1998 Elsaesser & Mannheim, astro-ph/0405235 Strong et al. 2004 E, MeV • Blazars • Cosmological neutralinos E, GeV

  25. B/C Be10/Be9 Zh increase Ek, MeV/nucleon Ek, MeV/nucleon Conclusions I Accurate measurements of nuclear species in CR, secondary antiprotons, and diffuse γ-rays simultaneously may provide a new vital information for Astrophysics – in broad sense, Particle Physics, and Cosmology. Hunter et al. region: l=300°-60°,|b|<10° Gamma rays: GLAST is scheduled to launch in 2007 – diffuse gamma rays is one of its priority goals Dark Matter CR species:New measurements at LE & HE simultaneously are highly desirable (Pamela, Super-TIGER, AMS…), also sec. positrons !

  26. Conclusions II Antiprotons: Pamela (2005), AMS (2008) and a new BESS-polar instrument to fly a long-duration balloon mission (in 2004, 2006…), we thus will have more accurate and restrictive antiproton data HE electrons:Several missions are planned to target specifically HE electrons We must be ready…! GALPROP is a propagation model to play now; the accuracy depends very much on the accuracy of the nuclear production cross sections

  27. Thank you !

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