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Fermi-LAT Study of Galactic Cosmic-Rays by Observing Diffuse Gamma-rays (Fermi 衛星による拡散 γ 線放射の観測と銀河系宇宙線 ) Tsunefumi Mizuno Hiroshima Univ. on behalf of the Fermi-LAT Collaboration ASJ 2009 Autumn Meeting September 15, 2009, Yamaguchi, Japan. SNR RX J1713-3946. B. HESS. π. 0. e. e.
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Fermi-LAT Study of Galactic Cosmic-Rays by Observing Diffuse Gamma-rays (Fermi衛星による拡散γ線放射の観測と銀河系宇宙線) Tsunefumi Mizuno Hiroshima Univ. on behalf of the Fermi-LAT Collaboration ASJ 2009 Autumn Meeting September 15, 2009, Yamaguchi, Japan
SNR RX J1713-3946 B HESS π 0 e e π gas gas + + + - - - Introduction 銀河宇宙線と拡散γ線放射 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 in distant locations 拡散γ線は宇宙線を探るプローブ
Fermi衛星による拡散γ線放射の観測 (1) : GMCs (e.g., Orion, Cham): matter distribution, correlation with mol. gas tracer : Mid/low-latitude region (EGRET GeV excess). submitted to PRL. See also ArXiv:0907.0294 : Mid/high-latitude region to study local CRs. (Abdo et al. 2009; contact: T. Mizuno) : Galactic plane (CR distribution in the MW) ~について、これまでの結果を簡単に紹介(次項) について若干詳しく
Fermi衛星による拡散γ線放射の観測 (2) : non-GeV-excess GeV-excessの否定 Preliminary EGRET LAT Orion MC (M~105Msun) :GMCs 物質分布 0.1 1 10 GeV Preliminary : local CRs 近傍の宇宙線はLISに酷似 LAT data model for the LIS nucleon-nucleon Cham MC (M~104Msun) electron-bremsstrahlung
銀河系内の宇宙線分布 • CR distribution in our Galaxy is a key to understand their origin and propagation • Distribution of SNRs not well measured • Previous Gamma-ray data suggests a flatter distribution than SNR/pulsar distributions (e.g., Strong et al. 2004) 宇宙線の空間分布は、起源・伝播を探る鍵 • Fermi-LAT is able to map out CR distributions in the Galaxy with unprecedented accuracy • Large scale analysis in progress. (arXiv:0907.0304) • We will focus on the preliminary analysis of the 3rd quadrant (outer Galaxy). See also the relevant study of the 2nd quadrant (arXiv:0907.0312) Gal. Center Inner Galaxy local arm Outer Galaxy 銀河系の外側の領域の結果の紹介 Perseus arm
Fermi-LATのカウントマップ • 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) 宇宙線分布の研究に適した領域 Preliminary Geminga Vela Crab Orion A/B Count Map (E>100 MeV)
G線 = 星間物質からの放射+点源 Local arm Perseus arm +2 HI maps (profile fitting technique; arXiv:0907.0312) + 詳細は林の講演参照(Q28a) • 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
G線スペクトル (~宇宙線スペクトル) HI Emissivity Spectrum of each ring (local arm) (interarm) (Perseus arm) Preliminary Point sources with Ts>=100 are included in the fitting 宇宙線陽子で1-100GeVに対応(主成分) • Emissivity (CR) spectrum of local arm (R=8.5-10 kpc) is slightly smaller than the model for LIS • Decreasing emissivity (local arm => interarm => Perseus arm) are consistent with decreasing CR density across the Galaxy • Similar CR spectral shape up to R=16 kpc • Can constrain the CR source distribution and propagation parameters • study in progress 宇宙線の強度分布・スペクトルが得られた モデルとの比較で宇宙線源や伝播に制限
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 • individual GMCs • non-GeV-excess • Mid/high-latitude region (local CRs) • large scale analysis (CR distribution throughout the Galaxy) • Preliminary analysis of the 3rd quadrant is disucssed • See also the relevant study of the 2nd quadrant • Similar CR spectral shape up to R=16 kpc • CR density gradient toward the outer Galaxy is obtained • Comparison with the CR source/propagation model prediction is in progress 拡散γ線放射は宇宙線を探るプローブ 様々な成果(分子雲,non-GeV-excess,近傍の宇宙線) 銀河系、とくに外側の領域で宇宙線分布があきらかになりつつある Thank you for your attention!
LAT vspre-Fermi Model • Compare with a CR propagation model prediction based on pre-Fermi CR data (Strong et al. 2004, Porter et al. 2008) • π0-decay, e-Brems, Inverse Compton • Source and isotropic (w/ residual BG) component come from fitting the data to the sky above 30 deg latitude with model fixed • Although there is a uniform excess above the model, data is reasonably reproduced by the model LAT model total Preliminary • p0-decay • e-Brems • IC The model is successful considering it is a priori pre-Fermi model
Probing CRs using Gamma-rays from ISM • Correlation with gas column density reveals the CR spectrum • Fermi-LAT’s high performance + CR propagation model (e.g. GALPROP) to predict IC • Sensitivity significantly improved Gamma-ray intensity (Fermi LAT data) ISM (e.g., LAB HI survey) (http://www.astro.uni-bonn.de/~webaiub/english/tools_labsurvey.php) • Mid/high latitude region & Galactic plane: • Study of the local CRs and CR gradient in the outer Galaxy (From Wikipedia) sun GC
Accurate Measurements of Local CRs (1) • Mid-high lat. region in 3rd quadrant: • small contamination of IC and molecular gas • correlate g-ray intensity and HI gas column density Abdo et al. 2009, accepeted by ApJ (arXiv:0908.1171) contact author: TM (error bars are statistical only) 400-560 MeV 1.6-2.3 GeV HI column density (1020 cm-2) 400-566 MeV E2 x g-ray Intensity HI column density (1020 cm-2)
Accurate Measurement of Local CRs (2) • Best quality g-ray emissivity spectrum in 100 MeV-10 GeV (Tp = 1-100 GeV) • Agree with the model prediction from the local interstellar spectrum (LIS) LAT data model from the LIS EGRET (Digel et al. 2001) nucleon-nucleon electron-bremsstrahlung 102 103MeV 104 • Prove that local CR nuclei spectra are close to those directly measured at the Earth • Eg<100 MeV constrain the e- spectrum
CR Flux Distribution LAT “measured” CR density SNR distribution by radio survey or traced by pulsar Preliminary • Emissivity gradient traces the CR density. Robust against the thresholds for point sources included. • Significantly flatter than the SNR distributions • may indicate more CR sources than previously thought in the outer Galaxy, large halo size, etc. • Comparison with the model prediction is in progress.
HI Maps R<=10-12.5 kpc R<=10 kpc R>=16 kpc R<=12.5-16 kpc
Wco Maps R<=10-12.5 kpc R<=10 kpc