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GALPROP & Modeling the Diffuse g -ray Emission

GALPROP & Modeling the Diffuse g -ray Emission. Modified from talk of Igor V. Moskalenko (Stanford U.). CR Interactions in the Interstellar Medium. SNR RX J1713-3946. 42 sigma (2003+2004 data). B. HESS Preliminary. PSF. π. 0. e. e. e. π. π. gas. gas. _. +. +. +. +. +.

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GALPROP & Modeling the Diffuse g -ray Emission

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  1. GALPROP & Modeling the Diffuse g-ray Emission Modified from talk of Igor V. Moskalenko (Stanford U.)

  2. CR Interactions in the Interstellar Medium SNR RX J1713-3946 42 sigma (2003+2004 data) B HESS Preliminary PSF π 0 e e e π π gas gas _ + + + + + - - - - - P ISM X,γ synchrotron Chandra IC ISRF P He CNO diffusion energy losses reacceleration convection etc. bremss GLAST p Flux LiBeB He CNO 20 GeV/n BESS • CR species: • Only 1 location • modulation PAMELA ACE AMS helio-modulation

  3. Diffuse Galactic Gamma-ray Emission ~80% of total Milky Way luminosity at HE !!! Tracer of CR (p, e−) interactions in the ISM (π0,IC,bremss): • Study of CR species in distant locations (spectra & intensities) • CR acceleration (SNRs, pulsars etc.) and propagation • Emission from local clouds → local CR spectra • CR variations, Solar modulation • May contain signatures of exotic physics (dark matter etc.) • Cosmology, SUSY, hints for accelerator experiments • Background for point sources (positions, low latitude sources…) • Besides: • “Diffuse” emission from other normal galaxies (M31, LMC, SMC) • Cosmic rays in other galaxies ! • Foreground in studies of the extragalactic diffuse emission • Extragalactic diffuse emission (blazars ?) may contain signatures of exotic physics (dark matter, BH evaporation etc.) Calculation requires knowledge of CR (p,e) spectra in the entire Galaxy

  4. Transport Equations ~90 (no. of CR species) ψ(r,p,t) – density per total momentum sources (SNR, nuclear reactions…) diffusion convection (Galactic wind) diffusive reacceleration (diffusion in the momentum space) E-loss radioactive decay fragmentation + boundary conditions

  5. Halo Gas, sources CR Propagation: Milky Way Galaxy 1kpc ~ 3x1018cm 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 “Flat halo” model (Ginzburg & Ptuskin 1976)

  6. What it takes to model CR propagation in the Galaxy • Gas distribution (energy losses, π0, brems) • Interstellar radiation field (IC, e± energy losses) • Nuclear & particle production cross sections • Gamma-ray production: brems, IC, π0 • Energy losses: ionization, Coulomb, brems, IC, synch • Assume propagation model (Dxx, Dp, Va) • Source distribution & injection spectra • Solve transport equations for all CR species • Fix propagation parameters

  7. More Effects: Local Environment Sun • Local Bubble: • A hole in the interstellar gas is formed in a series of SN explosions; some shocks may still exist there… • May be important for radioactive CR species, but Dxx=? Sun ~200pc Regular Galactic magnetic field may establish preferential directions of CR propagation GC

  8. CR Source Distribution Lorimer 2004 Pulsars SNR source CR after propagation diffuse γ-ray distribution The CR source (SNRs, pulsars) distribution is too narrow to match the CR distribution in the Galaxy assuming XCO=N(H2)/WCO=const (CO is a tracer of H2)

  9. Distribution of CR Sources & Gradient in the CO/H2 CR distribution from diffuse gammas (Strong & Mattox 1996) SNR distribution (Case & Bhattacharya 1998) Pulsar distribution Lorimer 2004 sun XCO=N(H2)/WCO: Histo –This work, Strong et al.’04 ----- -Sodroski et al.’95,’97 1.9x1020 -Strong & Mattox’96 ~Z-1 –Boselli et al.’02 ~Z-2.5 -Israel’97,’00, [O/H]=0.04,0.07 dex/kpc

  10. Electron Fluctuations/SNR stochastic events GeV electrons 100 TeV electrons GALPROP/Credit S.Swordy Electron energy loss timescale: 1 TeV: ~300 kyr 100 TeV: ~3 kyr Energy losses Bremsstrahlung E(dE/dt)-1,yr Ionization IC, synchrotron Coulomb 107 yr 1 GeV 1 TeV 106 yr Ekin, GeV

  11. Wherever you look, the GeV -ray excess is there ! EGRET data 4a-f

  12. Diffuse g-ray emission models Cosmic Ray Spectral Variations EGRET “GeV Excess” Dark Matter from Hunter et al. ApJ (1997) from Strong et al. ApJ (2004) from de Boer et al. A&A (2005) • There are two possible BUT fundamentally different explanations of the excess, in terms of exotic and traditional physics: • Dark Matter • CR spectral variations • Both have their pros & cons. 0.5-1 GeV >0.5 GeV

  13. GeV excess: Optimized/Reaccleration model antiprotons Uses all sky and antiprotons & gammas to fix the nucleon and electron spectra • Uses antiproton flux 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

  14. Diffuse Gammas at Different Sky Regions Hunter et al. region: l=300°-60°,|b|<10° Outer Galaxy: l=90°-270°,|b|<10° Inner Galaxy: l=330°-30°,|b|<5° corrected Intermediate latitudes: l=0°-360°,10°<|b|<20° l=40°-100°,|b|<5° Intermediate latitudes: l=0°-360°,20°<|b|<60° Milagro

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

  16. Latitude Profiles: Inner Galaxy 0.5-1 GeV 2-4 GeV 50-70 MeV 4-10 GeV 20-50 GeV

  17. Latitude Profiles: Outer Galaxy 0.5-1 GeV 50-70 MeV 2-4 GeV 4-10 GeV

  18. 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 ! Supersymmetry: • MSSM (DarkSUSY) • Lightest neutralino χ0 • mχ ≈ 50-500 GeV • S=½ Majorana particles • χ0χ0−> p, pbar, e+, e−, γ γ pbars e+

  19. Positions of the local clouds sun Pohl et al.2003 Digel et al.2001 The Excess: Clues from the Local Medium Observations of the local medium in different directions, e.g. local clouds, will provide a clue to the origin of the excess (assuming it exists). Inconclusive based on EGRET data Will GLAST see the excess? Yes No • Poor knowledge of • π0-production cross section: • better understanding of • π0-production • Dark Matter signal: • look for spectral signatures in cosmic rays (PAMELA, BESS, AMS) and in collider experiments (LHC) Possibility: cosmic-ray spectral variations. Further test: look at more distant clouds EGRET data

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