1. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 1 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. arXiv:0912.3618

2. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 2 Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays (1) e + - X,γ ISM diffusion energy losses energy losses reacceleration reacceleration convection convection etc. etc. π 0 synchrotron bremss HESS SNR RX J1713-3946 B Pulsar,  -QSO PHeCNO Chandra, Suzaku, Radio telescopes A powerful probe to study CRs in distant locations HE  -rays are produced via interactions between Galactic cosmic-rays (CRs) and the interstellar medium (or interstellar radiation field) IC ACTs and Fermi (see K. Hayashi’s talk) gas ISRF e + - π + - (CR accelerator) (Interstellar space) (Observer) (GMC is one of the best target matter) Pioneering theoretical works by Hayakawa (1952), Morrison (1958), etc.

3. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 3 Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays (2) Prediction of Gamma-rays  inverse Compton scattering (photon & CR electron)   0 -decay (matter & CR nucleon)  bremsstrahlung (matter & CR electron) GeV  -rays probes CR protons (and ISM)

4. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 4 Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays (3) Prediction of Gamma-rays  inverse Compton scattering (photon & CR electron)   0 -decay (matter & CR nucleon)  bremsstrahlung (matter & CR electron) GeV  -rays probes CR protons (and ISM)  0 component has a bump around 1 GeV in E 2 spectrum Fermi-LAT (E  ~ 0.1-10 GeV)  p =2  p =2.4 Local Interstellar Spectrum Aharonian 2004

5. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 5 Target: Interstellar Medium (Gas) Gas distribution determined from radio surveys  velocity => distance through a rotation curve G.C. 25° Clements(1985) (R 0,v 0 )=(8.5 kpc, 220 km/s) HI density from LAB survey  Opacity correction needed especially close to Gal. plane http://www.astro.uni-bonn.de/~webaiub/english/tools_labsurvey.php H 2 density from 2.6 mm CO line  assumptions on Xco=N(H 2 )/W CO Dame et al. 2001 target for producing gamma-rays through  0 -decay and electron bremsstrahlung 30° 0°0° -30°

6. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 6 Outstanding Question: EGRET GeV Excess (1) We can “measure” the CR spectrum in distant locations by observing diffuse  -rays. EGRET observations showed excess emission > 1 GeV everywhere in the sky when compared with models based on directly measured CR spectra Potential explanations  Dark Matter  Unexpectedly large variations in cosmic-ray spectra over Galaxy  Unresolved sources (pulsars, SNRs, …)  Instrumental Fermi-LAT is able to confirm or reject this phenomenon Hunter et al. 1997 ~100% difference above 1 GeV 0.1 1 10 GeV |b|=6°-10° |b|=2°-6° |b|<=2°

7. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 7 Outstanding Question: EGRET GeV Excess (2) We can “measure” the CR spectrum in distant locations by observing diffuse  -rays. EGRET observations showed excess emission > 1 GeV everywhere in the sky when compared with models based on directly measured CR spectra Potential explanations  Dark Matter  Unexpectedly large variations in cosmic-ray spectra over Galaxy  Unresolved sources (pulsars, SNRs, …)  Instrumental Fermi-LAT is able to confirm or reject this phenomenon Orion Region (Digel et al. 1999, Aharonian 2001) Data vs. model by E -2.1 spectrum

8. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 8 Intermediate Latitude Region seen by LAT (1) |b|=10°-20° 0.1 1 10 GeV EGRET LAT |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 GeV excess Strongly constrains the DM interpretation Abdo, A. A et al. Phys. Rev. Lett., 103, 251101 (2009)

9. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 9 Intermediate Latitude Region seen by LAT (2) 0.1 1 10 GeV EGRET LAT Abdo, A. A et al. Phys. Rev. Lett., 103, 251101 (2009) See also Abdo et al. 2009, ApJ 703, 1249 LAT spectrum is compatible with a prediction based on the LIS  0 is the dominant component 00 isotropic bremsstrahlung IC

10. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 10 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)

11. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 11 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 Gal. Center Inner Galaxy Outer 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 Recently accepted article (arXiv:0912.3618) discusses the  -rays in the the 2 nd quadrant Report on the relevant study in the 3 rd quadrant is in preparation local arm Perseus arm

12. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 12 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.

13. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 13 Extra galactic diffuse (uniform) Gamma-ray flux Inverse compton model map (galprop) Excess of E(B-V) map (Grenier et al. 2005) 2 HI maps 2 CO maps R=0-7.5kpc, 7.5-9.5kpc Data and Analysis Procedure Fit data at each energy bin : “(100~144 MeV), (144~200 MeV), …, (9.05~12.8 GeV)” Gamma-ray spectrum ( ) of each component Gamma-rays are modeled as a linear combination of each component

14. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 14 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  CR flux uncertainty, heavy nuclei in CRs and ISM

15. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 15 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  flatter CR source distribution and/or larger halo than previously thought  detailed discussion in forthcoming paper (3 rd quadrant, large-scale diffuse)

16. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 16 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

17. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 17 HI vs. CO Emissivities Gould Belt Local arm Perseus 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-H2 ratio (see next)

18. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 18 Xco Evolution Moderate evolution ov Xco (=N(H2)/Wco) is observed Could be due to the metallicity gradient Xco in outer Galaxy is much smaller than that inferred by the EGRET study

19. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 19 Summary Diffuse gamma-rays are powerful probe to study CRs and ISM in our Galaxy  Useful to constrain the CR protons EGRET GeV excess not confirmed  Strongly constrain the DM interpretation  Local CRs are compatible with those measured at the Earth Detailed study of the 2 nd quadrant  CRs and ISM in the outer Galaxy  Flatter CR gradient than previously assumed  Flatter but significant evolution of CO-to-H2 ratio  Relevant studies of the 3 rd quadrant and large-scale analysis in progress

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

21. 論文紹介 _2010-Jan.ppt Tsunefumi Mizuno 21 InterStellar Radiation Field CR e + /e - need targets to create g-rays  Interstellar radiation field determined from a realistic model taking into account stellar and dust distribution Starlight (~ 0.1  m – 10  m) Dust (~ 10  m – 300  m) CMB (>300  m) ISRF energy density R=0 kpc R=4 kpc R=8 kpc R=12 kpc CMB Dust Stellar There are uncertainties associated with gas and ISRF Porter et al. 2008