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Galactic Cosmic Rays

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  1. Galactic Cosmic Rays Igor V. Moskalenko Stanford & KIPAC

  2. Contents • Brief introduction to propagation of CRs • Direct measurements • Indirect measurements: diffuse gamma-ray emission • CR in other normal galaxies • Leptons in the heliosphere (Nicola Giglietto’s talk) • GALPROP: New and free service “webrun”. Registered users can run the considerably improved version of GALPROP on our new cluster (~200 cores and Terabytes of storage) using the Web interface. Goes on-line in the first week of August

  3. Introduction

  4. Halo Gas, sources CR Propagation: Milky Way Galaxy 1kpc~ 3×1021cm Optical image: Cheng et al. 1992, Brinkman et al. 1993 Radio contours: Condon et al. 1998 AJ 115, 1693 100 pc NGC891 50 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)

  5. SNR RX J1713-3946 42 sigma (2003+2004 data) Chandra B HESS HESS PSF π 0 ± ± ± e e e e π π Fermi gas gas _ _ + + + - - - P P CRs in the Interstellar Medium ISM X,γ synchrotron IC ISRF P He CNO •diffusion •energy losses •diffusive reacceleration •convection •production of secondaries bremss WIMP annihil. X,γ • P, p Flux LiBeB He CNO 20 GeV/n BESS • CR species: • Only 1 location • modulation ACE PAMELA helio-modulation

  6. Elemental Abundances: CR vs. Solar System “output” CR abundances: ACE Si Fe CNO Al Cl CrMn LiBeB F ScTiV Solar system abundances “input” Cosmic ray vs. solar system abundances, normalized to Si=100

  7. Secondary/primary nuclei ratio & CR propagation Typical parameters (model dependent): D ~ 1028 (ρ/1 GV)α cm2/s α≈ 0.3-0.6 Zh~ 4-6 kpc; VA ~ 30 km/s3 Be10/Be9 Interstellar Zh increase • Using secondary/primary nuclei ratio (B/C) & radioactive isotopes (e.g. Be10): • Diffusion coefficient and its index • Galactic halo size Zh • Propagation mode and its parameters (e.g., reacceleration VA, convection Vz) • Propagation parameters are model-dependent

  8. Secondary to primary nuclei ratios: B/C ratio The B/C ratio <30 GeV/n measured by Pamela is consistent with earlier measurements (no surprises) PAMELA Very preliminary! different model predictions models tuned to the data 0.3 Statistical errors only • Sparvoli’09 CREAM Ahn+’08 0.5 0.6 The propagation models’ predictions differ at high energies which will allow to discriminate between them when more accurate data are available

  9. Secondary to primary nuclei ratios: sub-Fe/Fe The rise in Ti/Fe ratio above ~100 GeV/nucleon is inconsistent with B/C ratio. Measurements of sub-Fe/Fe ratio is more challenging because of the smaller flux and charge is harder to discriminate Being tuned to one type of secondary/primary ratio (e.g. B/Cratio) propagation models should be automatically consistent with all secondary/primary ratios: • sub-Fe/Fe • He3/He4 • pbar/p (Sc+Ti+V)/Fe Ti/Fe Jones+’01 ATIC

  10. Diffusion coefficient in different models • The diffusion coefficient is model-dependent and is derived from secondary/primary nuclei ratio below ~100 GV • It is extrapolated above this energy ~R0.6 Plain diffusion ~β-3 Reacceleration with damping data extrapolation Diffusive Reacceleration (Kolmogorov) Ptuskin+’06

  11. Energy losses of nucleons • The ionization and Coulomb losses are calculated for the gas number density 0.01 cm-3 • The energy losses by nucleons can be neglected above ~1 GeV • Nuclear interactions are more important

  12. Total inelastic nuclear cross sections • The inelastic cross section gives a probability of interaction • Rises with the atomic number as ~A2/3 • As the result of interaction the original nucleus is destroyed Wellisch & Axen 1996 Ekin, MeV/nucleon

  13. Effective propagation distance: LE nuclei • The interaction time scale at ~1 GeV – 1 TeV: τ~ L/c ~ [σnc]-1 ~ 3×1013/[0.25 (A/12)2/3] s ~ 3×106 yr (A/12)-2/3 σCarbon(A=12) ≈ 250 mb • The diffusion coefficient (4 kpc halo): D ~ 3×1028 R1/2 cm2/s, R – rigidity in GV • Effective propagation distance: <X> ~ √6Dτ ~ 4.5×1021 R1/4 (A/12)-1/3 cm ~ 1.5 kpc R1/4 (A/12)-1/3 Helium: ~ 2.1 kpc R1/4 Carbon: ~ 1.5 kpc R1/4 0.36% of the surface area (25 kpc radius) Iron: ~ 0.9 kpc R1/40.16% (anti-) protons:~ 6 kpc R1/45.76% • γ-rays: probe CR p (pbar) and e± spectra in the whole Galaxy ~50 kpc across

  14. Direct probes of CR propagation • Direct measurements probe a very small volume of the Galaxy • The propagation distances are shown for rigidity ~1 GV Fe C p 50 kpc

  15. Energy losses of electrons • The ionization and Coulomb losses are calculated for the gas number density 0.01 cm-3 • Energy density of the radiation and magnetic fields 1 eV cm-3 (Thomson regime)

  16. Effective propagation distance: HE electrons • The energy loss time scale (IC) at ~1 GeV – 1 TeV: τ~ 300 E12−1kyr ~ 1013 E12−1s; E12 – energy in TeV • The diffusion coefficient: D ~ (0.5-1)×1030 E121/2 cm2/s • Effective propagation distance: <X> ~ √6Dτ ~ 5×1021 E12−1/4 cm ~ 1 kpc E12−1/4 ~ a few kpc at 10 GeV • The cutoff energy of the electron spectrum ~1 TeV can be used to estimate the distance to the local HE electron sources: ≥ a few 100 pc.

  17. Direct probes of CR propagation • Direct measurements probe a very small volume of the Galaxy • The propagation distances are shown for nuclei for rigidity ~1 GV, and for electrons ~1 TeV Fe, TeVe C p, 10 GeVe 50 kpc

  18. A Constellation of CR and gamma-ray (also CR!) instruments pbar đ,α e+ e- p He Z≤8 8<Z≤28 Z>28 WIMPs PAMELA BESS-Polar − anti-matter Integral WMAP HEAT CAPRICE AMS-I HESS Magic Milagro Veritas Fermi/LAT BESS-Polar AMS-I COMPTEL EGRET ACE ATIC CREAM matter HEAO-3 TRACER TIGER Fermi/LAT PAMELA BESS-Polar SUSY 1 MeV/n 1 TeV/n 1 GeV/n

  19. Direct measurements

  20. Recent experiments in cosmic rays • ATIC electrons (Chang+2008): 360+ • PPB-BETS electrons (Torii+2008): 150+ • Fermi LAT electrons (Abdo+2009): 310+ • HESS electrons (Aharonian+2008, 2009): 280+ • PAMELA positron fraction (Adriani+2009): 530+ leptons in CRs total: 1600+ citations in ~2 years! • PAMELA antiprotons (Adriani+2009): 240+ citations • BESS program (only journal papers): 1000+ citations Of course, most of citations are coming from particle physics ★ using NASA ADS/June 2010

  21. Positron fraction • The excess in the CR positron fraction relative to the predictions of secondary production models is confirmed by Pamela and extended to higher energies (up to ~100 GeV) • Additional positron component? • Charge sign dependence below ~10 GeV is expected Solar modulation GALPROP Adriani+’08

  22. Antiprotons − GALPROP - - Donato+’01 Antiprotons in CRs (BESS, Pamela) <200 GeV are in agreement with secondary production PAMELA PAMELA − GALPROP … Donato+’09 - - Simon+’98 Adriani+’10 Adriani+’10

  23. Fermi measurements of leptons in CR • Recently extended down to 7 GeV • High statistics: ~8M events (7 GeV – 1 TeV)in 1 year • Errors dominated by systematic uncertainties • No evidence of a prominent spectral feature • Analysis of events with high energy resolution in progress to confirm spectral shape Fermi What’s here? HESS

  24. Kobayashi+’03 Interpretation of CR electron data • CR electron spectrum is consistent with a single power-law with index -3.05 • Can be reproduced well by the propagation models • Multi-component interpretation is also possible • Dark matter contribution • Astrophysical sources (SNR, pulsars) • … The key to understanding the electron spectrum (local vs global) is the origin of the positron excess and the diffuse gamma-ray emission

  25. CR protons & He • The CR proton and He spectra by Pamela agree well with previous measurements • He spectrum is significantly flatter (~0.13 in index), but consistent with the proton index within the error bars • A hint on their different origin? • No surprises for production of secondary particles and diffuse gammas H: -2.752±0.071 He: -2.624±0.122 PAMELA Picozza’09 protons He IM+’02

  26. p and He spectral hardening at HE Statistically significant spectral hardening and heavier composition at HE is reported by ATIC and confirmed by CREAM CREAM Ahn+’10 ATIC Panov+’09

  27. Heavy nuclei at high energies • Ratios of the mostly primary nuclei are independent on the energy pointing to a similar origin and the same acceleration mechanism • The spectral slopes of He and heavier nuclei are the same at HE and flatter than protons • A significant fraction of N is secondary – steeper spectrum; about 10% is primary CREAM C/O N/O Ne/O Mg/O Si/O Fe/O Ahn+’10 Ahn+’10

  28. 20Ne 32S 53Mn* 40Ca 41Ca* 22Ne P F 55Mn 33S 15N ScTiV Good Xsections Well-known Differences in models CR source isotopic abundances • Two K-capture isotopes are present in the sources! --41Ca*, 53Mn* • Could tell us about the origin of CRs -- supports “volatility” hypothesis, but needs more analysis The first time that a realistic propagation model (GALPROP) has been used to derive isotopic source abundances ! Solar system Reacceleration Plain diffusion IVM+’07

  29. Cosmic ray sources • Some isotopes in CR sources are more abundant than in the solar system • May indicate that ~20% of CR particles are coming from WR star winds Binns+’05

  30. Heavy Nuclei in CRs • Produced in SN explosions • Abundances drop quickly with Z • Local: very large inelastic cross section – small effective propagation distances Fe Wiedenbeck+2007 Nucleus Charge

  31. The origin of cosmic rays • Cosmic ray acceleration seems to prefer refractory elements over volatile and does not depend on FIP, although most of refractory elements also have low ionization potential • Mixed with 20% of the WR wind outflow, the CR source composition/Solar system ratio shows a clear trend: ~A2/3 for volatile and ~A for refractory elements • This dependence is yet to be understood TIGER Rauch+’09

  32. Sources of high energy cosmic rays • A similar trend appears also at high energy, although with larger error bars • A single acceleration mechanism for LE and HE cosmic rays? CREAM Ahn+’10

  33. Fermi-LAT: First 3 Months Skymap (Counts) Indirect mearurements: Diffuse gamma-ray emission The diffuse emission is the brightest source on the sky: ~80% of all photons

  34. Milagro: TeV observations of Fermi sources Many γ-ray sources show extended structures at HE – thus they are also the sources of accelerated particles (CRs) unID (new TeV source) Fermi Pulsar MGRO 1908+06 HESS 1908+063 unID (new TeV source) Geminga pulsar Milagro C3 Radio pulsar (new TeV source) SNR IC433 MAGIC, VERITAS G.Sinnis’09 Pulsar (AGILE/Fermi) MGRO 2019+37 Fermi Pulsar SNR gCygni Fermi Pulsar HESS, Milagro, Magic Fermi Pulsar Milagro (C4) 3EG 2227+6122 Boomerang PWN G65.1+0.6 (SNR) Fermi Pulsar (J1958) New TeV sources SNR W51 HESS J1923+141

  35. Fermi-LAT: diffuse gammas • Conventional GALPROP model is in agreement with the Fermi-LAT data at mid-latitudes (mostly local emission) • The EGRET “GeV excess” is not confirmed • This means that we understand the basics of cosmic ray propagation and calculate correctly interstellar gas and radiation field, at least, locally model Abdo+’09

  36. Diffuse emission at low- to high Galactic latitudes • Pion-decay and inverse Compton emission are two dominant components – allow us to probe the average CR proton and electron spectra along the line of sight High latitudes Low latitudes Mid-latitudes • The GALPROP predictions agree well with the LAT data

  37. Diffuse Gammas – Local Spectrum • The spectrum of the local gas, after the subtraction of the IC emission, agrees well with the GALPROP predictions • Confirms that the local proton spectrum is similar to that derived from direct measurements Abdo+’09

  38. Milky Way as electron calorimeter • Calculations for Zhalo= 4 kpc • Leptons lose ~60% of their energy • γ-rays: 50-50 by nucleons and by leptons Cosmic rays 7.90×1040 erg/s Primarynucleons 98.6% Synchrotron 0.35% Ionization losses 1% • 0.29% (20.8%) • 0.06% (13.4%) Primary electrons 1.41% Secondary leptons • e+:0.33% • e−: 0.10% Bremsstrahlung 0.15% • 0.09% (6.6%) • 0.06% (13.5%) • 0.5% (34.8%) • 0.1% (21.1%) InverseCompton 0.58% • 0.59% (41.4%) • 0.16% (34.6%) Totalgamma rays 1.6% Neutralpions 0.85% * The percentages in brackets show the values relative to the luminosity of their respective lepton populations

  39. Other normal galaxies

  40. Cosmic rays in other normal galaxies (LMC) After background subtraction Milky Way LMC

  41. Starburst Galaxies: M82, NGC 253 The relationship between the gas mass, SNR rate, and gamma-ray luminosities in normal galaxies: LMC, Milky Way, M82, NGC 253 M82 NGC 253 MW LMC

  42. Thank you ! You are here