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Fermi-LAT Study of Galactic Cosmic-Ray Distribution -- CRs in the Outer Galaxy -- Tsunefumi Mizuno

Fermi-LAT Study of Galactic Cosmic-Ray Distribution -- CRs in the Outer Galaxy -- Tsunefumi Mizuno Hiroshima Univ. on behalf of the Fermi-LAT Collaboration ASJ 2010 Spring Meeting March 25, 2010, Hiroshima, Japan. Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays.

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Fermi-LAT Study of Galactic Cosmic-Ray Distribution -- CRs in the Outer Galaxy -- Tsunefumi Mizuno

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  1. Fermi-LAT Study of Galactic Cosmic-Ray Distribution -- CRs in the Outer Galaxy -- Tsunefumi Mizuno Hiroshima Univ. on behalf of the Fermi-LAT Collaboration ASJ 2010 Spring Meeting March 25, 2010, Hiroshima, Japan

  2. Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays HE g-rays are produced via interactions between cosmic-rays (CRs) and the interstellar medium (or the interstellar radiation field) Fermi-LAT (2008-present) 2.4p sr, 30 MeV-300 GeV • ISM distribution => CRs • those “measured” CRs => ISM A powerful probe to study CRs and ISM in distant locations

  3. LAT Study of the Galactic Diffuse Emission [1]: CR sources: SNRs, HESS unIDs (Katagiri et al., Hanabata et al.) [2]: ISM and possible CR sources: molecular clouds (Okumura et al., Sada et al.) Fermi-LAT all sky map (1yr) [3]: Galactic CRs: This talk (cf. Abdo et al. 2009, ApJ 703, 1249; Abdo et al. 2009, PL 103, 251101; Abdo et al. 2010, ApJ 710, 133)

  4. CR Distribution in Milky Way • CR distribution is a key to understand the CR origin and propagation • ISM gas distribution is traced by radio surveys + Galactic rotation • Then, Fermi-LAT is able to map out CR distributions in Milky Way with unprecedented accuracy • Detailed study of the outer Galaxy (2nd and 3rd quadrant) will be discussed. • Study of the whole Galaxy is in progress Gal. Center Inner Galaxy Outer Galaxy

  5. CR Distribution in the Outer Galaxy(2nd Quadrant) • CR distribution is a key to understand the CR origin and propagation • ISM gas distribution is traced by radio surveys + Galactic rotation • Then, Fermi-LAT is able to map out CR distributions in Milky Way with unprecedented accuracy Gal. Center Inner Galaxy Gould Belt R=8.8 kpc local arm Outer Galaxy R=10 kpc Perseus arm outer arm Abdo et al. 2010 (ApJ 710, 133) Contact: L. Tibaldo, I. Grenier R=14 kpc

  6. CR Distribution in 2nd Quadrant g-ray emissivity (per H-atom) • The shape of CR spectrum in Gould Belt (d<=300 pc) is close to those measured at the Earth pion-dacay model (scaled) Bremsstrahlung 200 MeV g-ray intensity profile GALPROP prediction using PSR distribution as input sources • Decrease of CR densities with gradient flatter than expectations for SNR sources as traced by PSR • Property of molecular clouds is also discussed in paper Fermi data

  7. CR Distribution in the Outer Galaxy (3rd Quadrant) • CR distribution is a key to understand the CR origin and propagation • ISM gas distribution is traced by radio surveys + Galactic rotation • Then, Fermi-LAT is able to map out CR distributions in Milky Way with unprecedented accuracy Gal. Center Inner Galaxy outer arm R=16 kpc Outer Galaxy Perseus arm R=12.5 kpc inter arm R=10 kpc local arm

  8. CR Distribution in 3rd Quadrant g-ray emissivity (per H-atom) • Spectral shape agrees well with the model for the LIS, and no significant spectral shape variation is observed. • CR spectrum in Tp~1-100 GeVdoes not vary significantly in the region studied Preliminary g-ray intensity profile Preliminary • Consistent view of CR density gradient: Decrease of CR densities with gradient flatter than expectations by a conventional model Fermi data GALPROPprediction using SNR distribution (Case & Bhattacharya 1998)

  9. Possible Scenario of CR Density Distribution • We ran GALPROP to search a possible scenario to explain the flat CR density distribution obtained by the LAT • Large halo size is required to reproduce the LAT data • Or, a flat source distribution in the outer Galaxy is required test of several halo sizes test of a flat CR source distribution in R>Rbk Preliminary Zh = 1, 2, 4, 10, 15, 20 kpc Rbk = 10, 11, 12, 13, 14, 15 kpc • A larger halo size and/or a flatter CR source distribution than those by a conventional models are required • Other scenarios may also explain the observed profile (e.g., Evoli et al. 2008)

  10. Summary • Diffuse gamma-ray emission is a powerful probe to study the CR (and matter) distribution in distant locations in our Galaxy • Extensive analysis by Fermi-LAT is in progress • CR sources (Katagiri et al., Hanabata et al.) • individual GMCs (Okumura et al., Sada et al.) • non-GeV-excess, mid/high-latitude region (local CRs) • large scale analysis (CR distribution throughout the Galaxy) • Detailed study of the outer Galaxy is discussed • Flatter CR density gradient than a conventional model toward the outer Galaxy • Flat CR source distribution and/or a large CR halo is a possible scenario Thank you for your attention!

  11. Backup Slides

  12. CR Distribution in 3rd Quadrant Preliminary Preliminary • Spectral shape agrees well with the model for the LIS, and no significant spectral shape variation is observed. • CR spectrum in Tp~1-100 GeVdoes not vary significantly in the region studied

  13. Fermi-LAT View of the 3rd Quadrant • One of the best studied regions in g-rays • Vela, Geminga, Crab and Orion A/B • Galactic plane between Vela and Geminga (green square) is ideal to study diffuse g-rays and CRs. • small point source contamination, kinematically well-separated arms (local arm and Perseus arm) Preliminary Geminga Vela Crab Orion A/B Count Map (E>100 MeV)

  14. Construction of the Model Local arm Perseus arm +2 HI maps (profile fitting technique; arXiv:0907.0312) + • Fit g-ray data with 8 maps + 15 point sources (11 month source list) • CR spectrum (g-ray emissivity) is assumed to be uniform in each Galactocentric ring Preliminary Local arm + 1 CO map + excess E(B-V) map (Grenier et al. 2005) + IC map (galprop model) + point sources (11 month list) I(E, l, b) = SA(E)*HI(l,b) + SB(E)*Wco(l,b) +Sothers+Spoint_sources

  15. SNR RX J1713-3946 B HESS π 0 e e π gas gas + + + - - - Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays HE g-rays are produced via interactions between Galactic cosmic-rays (CRs) and the interstellar medium (or interstellar radiation field) (CR accelerator) (Interstellar space) (Observer) ISM X,γ synchrotron Chandra, Suzaku, Radio telescopes IC ISRF P He CNO diffusion energy losses reacceleration convection etc. bremss Pulsar, m-QSO ACTs and Fermi (see K. Hayashi’s talk) (GMC is one of the best target matter) Pioneering theoretical works by Hayakawa (1952), Morrison (1958), etc. A powerful probe to study CRs and ISM in distant locations

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