glast2003

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Published on October 31, 2007

Author: Chyou

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Slide1:  Propagation of CR electrons and the interpretation of diffuse rays Andy Strong MPE, Garching GLAST Workshop, Rome, 17 Sept 2003 with Igor Moskalenko & Olaf Reimer Slide2:  * What's new in interpretation of EGRET diffuse -rays * origin of the GeV excess * => implications for CR electrons * New extragalactic spectrum Slide3:  WMAP will provide constraints on electron propagation (23 – 94 Ghz) 408 Mhz Haslam 23 GHz WMAP 408 MHz/23 Ghz spectral index Spectral steepening: direct evidence for electron propagation from disk to halo Excellent data for testing electron propagation models Bennett et al. (2003) ApJS 148, 97 Direct evidence for Galactic electrons Slide4:  Casadei, ICRC 2003 normalized at 20 GeV Hams et al. ICRC2003 BESS 1999: normalized Still uncertainty in absolute fluxes even at 1-10 GeV ! Direct electron measurements Slide5:  Computing diffuse -rays galprop model 2D / 3D / equilibrium / time dependent, stochastic sources CR propagation: primary, secondary, e+, p- etc. Injection -- diffusion -- convection-- energy-loss – reacceleration -rays : using HI, CO, interstellar radiation field Slide6:  Electrons: propagation complex due to rapid losses Interstellar radiation field not well enough known can improve with e.g. WMAP data big project, but required for GLAST-quality data Local electron spectrum may not be good guide Time-dependent model needed. Interstellar radiation field R = 4 kpc R= 8 kpc R kpc eV cm-3 Slide7:  Electron energy losses large at low and high energy < 100 MeV ionization > 1 GeV inverse Compton, synchrotron  rays from bremsstrahlung < 1 GeV, less than originally thought minor role? Eelectron~ Egamma 10-1000 MeV, hard to observe – solar modulation true situation at low energies very uncertain Slide8:  Normal electron spectrum leads to well-known discrepancy (GeV excess) Is it the CR spectrum or could it be due to sources (e.g. SNR show the particle injection spectrum – hard) Hard proton spectrum ? : excluded using secondary positrons, antiprotons! Strong, Moskalenko,Reimer ICRC 2003 astroph/0306346 Slide9:  Excess present also in outer Galaxy and high latitudes => source hypothesis unlikely -> need hard electron spectrum Slide10:  Hard electron injection spectrum improves fit and away from inner Galaxy is satisfactory Slide11:  Hard electron injection spectrum (E-1.9) can improve fit but still require another component for inner Galaxy (SNR ?) Milagro 20o< l <100o 3 TeV cutoff in electron injection Slide12:  Milagro, inner Galaxy Fleysher 28th ICRC 2003 8 +- 3.3 10-10 cm-2 sr-1 s-1 > 1 TeV for E-2.63 Need cutoff in electrons at few TeV to avoid too much IC Slide13:  In this scenario, inverse Compton dominates at low energies and equals o-decay at high energies Testable by GLAST  o Slide14:  Latitude distribution can distinguish inverse Compton (also effect on estimates of extragalactic background)  o  o Slide15:  SNR Electron spectra from non-linear shock models by Ellison et al. 2000 ApJ 540, 292: hard spectrum to ~ TeV with TeV cutoff as required by diffuse -rays! NB this is spectrum in SNR, but what is spectrum of escaping electrons which give diffuse 's? Slide16:  Strong & Moskalenko ICRC2001 1 GeV 16 GeV 130 GeV 1 TeV Effect of stochastic SNR on electron distribution Slide17:  Electron spectrum fluctuates with position Locally measured Depends on SN rate High rate 1/104 yr/kpc3 Low rate1/105 yr/kpc3 Fluctuations not enough to explain -ray GeV excess! Slide18:  Inverse Compton shows fluctuations reflecting stochastic SNR Should be detectable by GLAST 1 GeV 1 TeV Slide19:  RED Shell-type (D. Green) BLUE Plerion-type (Kobayashi et al.) 1TeV 10TeV 100TeV Swordy, ICRC 2003 Slide20:  Yoshida ICRC 2003 Kobayashi astroph/0308470 Electrons from nearby/recent SNR r ~ √Dt For SNR younger than 105 yr only >TeV electrons have reached us even for distance 300 pc. Cutoff by energy losses. Only Vela, Monogem, Cygnus Loop may give individual signatures. D ~ E0.3-0.6 dE/dt ~ E2 Slide21:  Below 100 MeV not clear if CR or source population Electron energy losses large < 100 MeV ionization  rays from bremsstrahlung < 1 GeV, less than originally thought -minor role? Eelectron~ Egamma 10-1000 MeV, hard to observe – solar modulation intersellar spectrum at low energies very uncertain LOW ENERGIES < 30 MeV Slide22:  Solar modulation of electrons: Computed electron spectra (Galactic + Jovian) for Ulysses Ferreira et al. 2003 ApJ 594, 552 1 AU 90 AU 60 AU 5 AU Slide23:  Pulsar distribution: Lorimer IAU 218, (2003) astroph/030850 914 pulsars Pulsars max/solar = 3.3 cf. gammas ~ 1 Better determined than SNR. The classical gradient problem for SNR origin is still with us! pulsars CR/gammas Slide24:  Sources: Pulsar distribution from Lorimer (2003) Gamma-ray longitude profiles 300-500 MeV total IC  o IC bremss Sources: fitted to 's  o IC bremss Slide25:  New estimate of extragalactic diffuse spectrum in EGRET range using galprop model of Galactic emission Sreekumar Strong, Moskalenko, Reimer 2003 28th ICRC astroph/0306345 Difference mainly due to larger Galactic inverse Compton emission X X X Slide26:  E N D

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