2010 Jan ppt Fermi Tsunefumi Mizuno Hiroshima Univ

論文紹介_2010 -Jan. ppt Fermi衛星でみた拡散ガンマ線放射と銀河宇宙線 Tsunefumi Mizuno Hiroshima Univ. June 15, 2009 "Fermi Large Area Telescope Measurements of the Diffuse Gamma-Ray Emission at Intermediate Galactic Latitudes": Abdo, A. A et al. Phys. Rev. Lett. , 103, 251101 (2009) "Fermi observations of Cassiopeia and Cepheus: diffuse gamma-ray emission in the outer Galaxy" Abdo, A. A. et al. ar. Xiv: 0912. 3618 Tsunefumi Mizuno 1

Introduction 論文紹介_2010 -Jan. ppt Cosmic-Rays and Galactic Diffuse Gamma-Rays (1) HE g-rays are produced via interactions between Galactic cosmic-rays (CRs) and the interstellar medium (or interstellar radiation field) (CR accelerator) SNR RX J 1713 -3946 (Interstellar space) X, γ e (Observer) ISM otron r h c syn + - Chandra, Suzaku, Radio telescopes B HESS Pulsar, m-QSO P diffusion He energy losses CNO reacceleration + convection e + etc. π- (GMC is one of the best target matter) gas ISRF gas IC s brems π0 ACTs and Fermi (see K. Hayashi’s talk) Pioneering theoretical works by Hayakawa (1952), Morrison (1958), etc. A powerful probe to study CRs in distant locations Tsunefumi Mizuno 2

Introduction 論文紹介_2010 -Jan. ppt Cosmic-Rays and Galactic Diffuse Gamma-Rays (2) • Prediction of Gamma-rays Ø inverse Compton scattering (photon & CR electron) Ø p 0 -decay (matter & CR nucleon) Ø bremsstrahlung (matter & CR electron) • Ge. V g-rays probes CR protons (and ISM) Tsunefumi Mizuno 3

Introduction 論文紹介_2010 -Jan. ppt Cosmic-Rays and Galactic Diffuse Gamma-Rays (3) • Prediction of Gamma-rays Ø inverse Compton scattering (photon & CR electron) Ø p 0 -decay (matter & CR nucleon) Ø bremsstrahlung (matter & CR electron) • Ge. V g-rays probes CR protons (and ISM) p 0 component has a bump around 1 Ge. V in E 2 spectrum Gp=2 Fermi-LAT (Eg ~ 0. 1 -10 Ge. V) Gp=2. 4 Local Interstellar Spectrum Aharonian 2004 Tsunefumi Mizuno 4

論文紹介_2010 -Jan. ppt Target: Interstellar Medium (Gas) • Gas distribution determined from radio surveys Øvelocity => distance through a rotation curve HI density from LAB survey ØOpacity correction needed especially close to Gal. plane 25° G. C. Clements(1985) (R 0, v 0)=(8. 5 kpc, 220 km/s) http: //www. astro. uni-bonn. de/~webaiub/english/tools_labsurvey. php 30° Dame et al. 2001 0° H 2 density from 2. 6 mm CO line Øassumptions on Xco=N(H 2)/WCO -30° target for producing gamma-rays through p 0 -decay and electron bremsstrahlung Tsunefumi Mizuno 5

Outstanding Question: 論文紹介_2010 -Jan. ppt EGRET Ge. V Excess (1) • We can “measure” the CR spectrum in distant locations by observing diffuse grays. • EGRET observations showed excess emission > 1 Ge. V everywhere in the sky when compared with models based on directly measured CR spectra • Potential explanations Ø Dark Matter Ø Unexpectedly large variations in cosmic-ray spectra over Galaxy Ø Unresolved sources (pulsars, SNRs, …) Ø Instrumental • Fermi-LAT is able to confirm or reject this phenomenon Tsunefumi Mizuno |b|=6°-10° 0. 1 1 10 Ge. V |b|=2°-6° |b|<=2° ~100% difference above 1 Ge. V Hunter et al. 1997 6

Outstanding Question: 論文紹介_2010 -Jan. ppt EGRET Ge. V Excess (2) • We can “measure” the CR spectrum in distant locations by observing diffuse grays. • EGRET observations showed excess emission > 1 Ge. V everywhere in the sky when compared with models based on directly measured CR spectra • Potential explanations Ø Dark Matter Ø Unexpectedly large variations in cosmic-ray spectra over Galaxy Ø Unresolved sources (pulsars, SNRs, …) Orion Region Ø Instrumental • Fermi-LAT is able to confirm or reject this phenomenon Tsunefumi Mizuno (Digel et al. 1999, Aharonian 2001) Data vs. model by E-2. 1 spectrum 7

論文紹介_2010 -Jan. ppt Intermediate Latitude Region seen by LAT (1) |b|=10°-20° EGRET LAT Abdo, A. A et al. Phys. Rev. Lett. , 103, 251101 (2009) 0. 1 1 10 Ge. V • |b|=10°-20°: avoid Galactic Plane, high statistics and high S/N ratio (Extragalactic diffuse) • EGRET spectrum extracted for the same region • LAT spectrum is significantly softer and does not confirm the EGRET Ge. V excess • Tsunefumi Strongly constrains the DM interpretation Mizuno 8

論文紹介_2010 -Jan. ppt Intermediate Latitude Region seen by LAT (2) Abdo, A. A et al. Phys. Rev. Lett. , 103, 251101 (2009) See also Abdo et al. 2009, Ap. J 703, 1249 EGRET LAT p 0 isotropic bremsstrahlung Tsunefumi Mizuno 0. 1 IC 1 10 Ge. V • LAT spectrum is compatible with a prediction based on the LIS • p 0 is the dominant component 9

論文紹介_2010 -Jan. ppt Possible Cause of EGRET/LAT Discrepancy • EGRET also showed significantly harder spectrum for Vela Pulsar (BG negligible). • Could be due to Calibration uncertainty (large correction for backsplash) Tsunefumi Mizuno 10

論文紹介_2010 -Jan. ppt CR Distribution in Galaxy • CR distribution in our Galaxy is a key for understanding their origin and propagation • Distribution of SNRs not well measured • Fermi-LAT is able to map out CR distributions in the Galaxy • LAT data in the 2 nd and 3 rd Galactic quadrant provide us with accurate measurement of CR density distributions in the outer Galaxy Gal. Center Inner Galaxy • Recently accepted article (ar. Xiv: 0912. 3618) discusses the g-rays in the 2 nd quadrant local arm Outer Galaxy • Report on the relevant study in the 3 rd quadrant is in preparation Perseus arm Tsunefumi Mizuno 11

論文紹介_2010 -Jan. ppt Gas Density Distribution • Simple slicing using the rotation curve is not good enough to fully exploit the LAT data • Region boundaries are shifted to the intensity minima • Fit the profile with gaussians and apply spillover correction. Tsunefumi Mizuno 12

論文紹介_2010 -Jan. ppt Data and Analysis Procedure Gamma-ray flux 2 HI maps R=0 -7. 5 kpc, 7. 5 -9. 5 kpc Extra galactic diffuse (uniform) Inverse compton model map (galprop) Excess of E(B-V) map (Grenier et al. 2005) 2 CO maps Gamma-rays are modeled as a linear combination of each component Fit data at each energy bin : “(100~144 Me. V), (144~200 Me. V), … , (9. 05~12. 8 Ge. V)” Gamma-ray spectrum ( ) of each component Tsunefumi Mizuno 13

論文紹介_2010 -Jan. ppt Local HI (CR) Spectrum • Local HI spectrum (Gould Belt) is well represented by the interaction of CRs and ISM • Absolute intensity is ~50% larger than the galprop model Ø CR flux uncertainty, heavy nuclei in CRs and ISM Tsunefumi Mizuno 14

論文紹介_2010 -Jan. ppt Emissivity (CR density Gradient) • Galprop model is based on CR source distribution (traced by pulsars) and conventional CR propagation model (e. g. , CR halo of 4 kpc) • Measured gradient is flatter than the model Ø flatter CR source distribution and/or larger halo than previously thought Ø detailed discussion in forthcoming paper (3 rd quadrant, large-scale diffuse) Tsunefumi Mizuno 15

論文紹介_2010 -Jan. ppt Emissivity Spectrum in Outer Galaxy • HI spectral ratio to that of Gould Belt • Possible spectral hardening is observed (not seen in the 3 rd quadrant) • Systematic uncertainty (unresolved sources, etc. ) not ruled out Local arm to Gould Belt Perseus arm to Gould Belt Tsunefumi Mizuno 16

論文紹介_2010 -Jan. ppt HI vs. CO Emissivities Gould Belt Perseus arm Tsunefumi Mizuno Local arm • HI emissivity vs. CO emissivity of 3 regions • Proportionality supports the idea that CRs penetrate to the core of molecular clouds • Different slope indicate evolution of CO-to-H 2 ratio (see next) 17

Xco Evolution 論文紹介_2010 -Jan. ppt • Moderate evolution ov Xco (=N(H 2)/Wco) is observed • Could be due to the metallicity gradient • Xco in outer Galaxy is much smaller than that inferred by the EGRET study Tsunefumi Mizuno 18

Summary 論文紹介_2010 -Jan. ppt • Diffuse gamma-rays are powerful probe to study CRs and ISM in our Galaxy Ø Useful to constrain the CR protons • EGRET Ge. V excess not confirmed Ø Strongly constrain the DM interpretation Ø Local CRs are compatible with those measured at the Earth • Detailed study of the 2 nd quadrant Ø CRs and ISM in the outer Galaxy Ø Flatter CR gradient than previously assumed Ø Flatter but significant evolution of CO-to-H 2 ratio Ø Relevant studies of the 3 rd quadrant and large-scale analysis in progress Tsunefumi Mizuno 19

論文紹介_2010 -Jan. ppt HI Emissivity Spectra Gould Belt Local arm Perseus arm Tsunefumi Mizuno 20

論文紹介_2010 -Jan. ppt Inter. Stellar Radiation Field • CR e+/e- need targets to create g-rays ØInterstellar radiation field determined from a realistic model taking into account stellar and dust distribution üStarlight (~ 0. 1 mm – 10 mm) üDust (~ 10 mm – 300 mm) ISRF energy density üCMB (>300 mm) R=0 kpc There are uncertainties associated with gas and ISRF R=4 kpc R=8 kpc R=12 kpc Stellar Dust CMB Porter et al. 2008 Tsunefumi Mizuno 21