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Modeling of the Galactic diffuse continuum γ -ray emission

Modeling of the Galactic diffuse continuum γ -ray emission. Igor V. Moskalenko (Stanford U.) with A.Strong (MPE), S.Digel (SLAC), T.Porter (USCS), O.Reimer (SU). Simulated LAT (>1 GeV, 1 yr). GLAST Large Area Telescope (LAT).

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Modeling of the Galactic diffuse continuum γ -ray emission

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  1. Modeling of the Galactic diffusecontinuum γ-ray emission Igor V. Moskalenko (Stanford U.) with A.Strong (MPE), S.Digel (SLAC), T.Porter (USCS), O.Reimer (SU)

  2. Simulated LAT (>1 GeV, 1 yr) GLAST Large Area Telescope (LAT) This is an animation that steps from 1. EGRET (>100 MeV), to 2. LAT (>100 MeV), to 3. LAT (>1 GeV) EGRET (>100 MeV) Seth Digel

  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: • 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. 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

  5. A Model of CR Propagation in the Galaxy • Gas distribution (Leiden-Argentina-Bonn HI, CfA CO surv.) • Interstellar radiation field (87 stellar classes, gas, dust, including heating and re-emission) • Source distribution (SNR, pulsars) • Nuclear & particle production cross sections (LANL, Webber) • Gamma-ray production: brems, IC, π0 • Energy losses: ionization, Coulomb, brems, IC, synch • Solve transport equations for all CR species (~90!) • Fix propagation parameters

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

  7. Antiproton flux B/C ratio B/C ratio Antiproton flux Reacceleration Model vs. Plain Diffusion Plain Diffusion (Dxx~β-3R0.6) Diffusive Reacceleration

  8. More excesses: Positron Excess ? HEAT (Beatty et al. 2004) e+/e e+/e E > 6 GeV GALPROP HEAT 2000 HEAT 1994-95 HEAT combined GALPROP 10 1 1 10 E, GeV E, GeV Q: Are all the excesses connected? A: “Yes” and “No” Systematic errors of different detectors Same progenitor (CR p or DM) for pbars, e+’s, γ’s… or a local positron source?

  9. 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 Ek, GeV protons electrons x4 x1.8 Ek, GeV Ek, GeV

  10. Secondary e± are seen in γ-rays ! In the heliosphere: e+/e~0.2 In the Galaxy: e+/e~1 <1 GeV electrons sec. IC positrons brems Improves an agreement in MeV range

  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. Gas Rings: HI (Our Neighborhood) Latitude Seth Digel’05 Longitude

  13. R= 0 kpc 4 kpc 8 kpc 12 kpc 16 kpc Local ISRF stars CMB IR Interstellar radiation field scattered • The ISRF plays an important role: • Generation of Galactic diffuse -ray emission (IC) • IC energy losses of electrons and positrons • It is very intense in the Galactic center • Attenuation of TeV -ray sources (see Poster 18C !)

  14. Anisotropic Inverse Compton Scattering • Electrons in the halo see anisotropic radiation • Observer sees mostly head-on collisions Energy density e- R=4 kpc small boost & less collisions e- head-on: large boost & more collisions Z, kpc γ γ γ Important @ high latitudes ! sun

  15. Effect of anisotropic ICS Ratio anisoIC/isoIC pole anti-GC Intermediate latitudes GC • The anisotropic IC scattering plays important role in modeling the Galactic diffuse emission • Affects estimates of isotropic extragalactic background Galactic latitude, degrees

  16. 0 Total EG isoIC bremsstrahlung Latitude Latitude profile of the outer Galaxy anisotropic IC • The aniso IC is maximal (x2) in the outer Galaxy around b=20-30 • Agreement with data impossible without aniso IC

  17. G+EG EGRET G+EG COMPTEL G COMPTEL (Strong’99) INTEGRAL (Strong’05) anisoIC G+EG isoIC Positronium + sources?? Total Galactic EG COMPTEL (Weidenspointner’00) EG EGRET (Strong’04) Diffuse emission from the inner Galaxy Extragalactic ASCA HEAO A2 HEAO A4 EGRET COMPTEL • The “optimized” model describes the spectrum of the diffuse emission from MeV to TeV energies • Predictions down to keV’s (note, INTEGRAL data include positronium continnum) • MeV region appears to be transitional between Galactic and EG emission dominance

  18. Conclusions • We are building a model of the diffuse emission preparing for the GLAST mission • The diffuse emission model becomes more realistic now with more prediction capability outside the MeV-GeV region • MeV region is transitional (Galactic vs. extragalactic dominance) • On the other hand, GLAST will resolve 1000’s of unresolved sources putting stricter constraints on the diffuse emission model • Prepare to see unexpected ! • This will have an impact on CR studies, derivation and interpretation of the extragalactic background, and will possibly affect the dark matter studies

  19. Diffuse emission from the outer Galaxy anisotropic IC isoIC bremss

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