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Diffuse Galactic  -ray emission model

Diffuse Galactic  -ray emission model. Igor V. Moskalenko (Stanford) with S. Digel (SLAC) T. Porter (UCSC) O. Reimer (Stanford) A. W. Strong (MPE). Diffuse Galactic Gamma-ray Emission. ~80% of total Milky Way luminosity at HE !!!

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Diffuse Galactic  -ray emission model

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  1. Diffuse Galactic -ray emission model Igor V. Moskalenko (Stanford) with S. Digel (SLAC) T. Porter (UCSC) O. Reimer (Stanford) A. W. Strong (MPE)

  2. 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

  3. Conventional model vs EGRET data 0 IC Bremss EG Conventional model consistent with local p,e spectra exhibits the “GeV excess:” a factor ~2 We must have at least 2 diffuse emission models with/without the excess 4a-f

  4. DC2 diffuse emission model • galprop ID = 6002029RB • Based on • Strong,Moskalenko,Reimer, 2004, ApJ 613,962 • Strong,Moskalenko,Reimer,Digel,Diehl, 2004, A&A 422, L47 • Optimized to fit EGRET data (GeV excess: CR spectra) • Includes secondary electrons & positrons • Pulsar/SNR source distribution • Gradient in X-factor (H2/CO) • Improvements: • new HI, CO data (Digel) • new interstellar radiation field (Porter) • fine adjustments to reflect these new inputs • Examples of model unconvolved and convolved with EGRET PSF

  5. GeV excess: Optimized/Reaccleration 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 • pbars • e+ -flux • γ-rays Ek, GeV protons electrons Strong etal 2004 x4 x1.8 Ek, GeV Ek, GeV

  6. Secondary e± are seen in γ-rays ! Lots of new effects ! electrons Heliosphere: e+/e~0.2 sec. IC positrons brems Improves an agreement at LE

  7. Distribution of interstellar gas • Neutral interstellar medium – most of the interstellar gas mass • 21-cm H I & 2.6-mm CO (standing for H2) • Differential rotation of the Milky Way – plus random motions, streaming, and internal velocity dispersions – is largely responsible for the spectrum • This is the best – but far from perfect – distance measure available • Self-absorption of HI (21cm) and optical depth effects… (25°, 0°) CO 25° Dame et al. (1987) G.C. H I Hartmann & Burton (1997) W. Keel

  8. New H2 maps (S.Digel)

  9. New HI maps (S.Digel)

  10. Interstellar Radiation Field Local ISRF (PS05) Old model • Target for CR leptons (IC) • Energy losses Optical IR • Model components: • Geometrical: disk, ring, halo, bar, triaxial bulge, arms • 87 stellar types (main sequence), AGB & exotics • Dust: silicate, graphite, PAH (5Å – few m) • Absorbed light gives mid-IR (small grains +PAH) and FIR (~0.1-1 m grains) PAH Scatt.opt. SMR00 PS05 R=0 4 kpc • Systematic errors: • Star distribution –star counts • Grain properties –lab measurements • Gas/dust proportion –extinction curve • “Reasonable parameters” • Compare with ISRF data only at R 12 kpc 16kpc

  11. 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

  12. Inner Galaxy region Comparison with EGRET & COMPTEL spectral data Other regions demonstrate equally good agreement

  13. Model comparison with data • Convolution with EGRET PSF: • Important below 1 GeV • A large effect at low energies especially in latitude affecting the overall spectral shape • Convolution itself is model dependent -depends on spectrum, not fully accounted for

  14. Effect of Convolution: 70-100 MeV Longitude profile |b|<5 Unconvolved Convolved

  15. Effect of Convolution: 70-100 MeV Latitude profile |l|<30 Unconvolved Convolved

  16. Effect of Convolution: 0.5-1 GeV Longitude profile |b|<5 Unconvolved Convolved

  17. Effect of Convolution: 0.5-1 GeV Latitude profile |l|<30 Unconvolved Convolved

  18. 1-2 GeV 1000 – 2000 MeV Convolution effect is negligible

  19. Effect of De-Convolution: Spectrum |l|<30 |b|<5 “Convolved data” De-convolved NB here the spatialconvolution correction isapplied to the DATA based on the model. Hence the DATA changes, not the model (procedure appropriate for spectra)

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