論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 1
FermiFermi 衛星でみた拡散ガンマ線放射と銀河宇宙線衛星でみた拡散ガンマ線放射と銀河宇宙線
Tsunefumi MizunoTsunefumi MizunoHiroshima Univ.Hiroshima Univ.
June 15, 2009June 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-rayemission in the outer Galaxy"
Abdo, A.A. et al.arXiv:0912.3618
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 2
Introduction Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays (1)Cosmic-Rays and Galactic Diffuse Gamma-Rays (1)
e+-
X,γISM
diffusiondiffusion energy losses energy losses reaccelerationreacceleration convectionconvection etc.etc.
π0
synchrotron
bremssHESS
SNR SNR RX J1713-3946RX J1713-3946
B
Pulsar,-QSO
PPHeHeCNOCNO
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
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.
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 3
Introduction Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays (2)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)
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 4
Introduction Introduction Cosmic-Rays and Galactic Diffuse Gamma-Rays (3)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 E2 spectrum
Fermi-LAT(E~ 0.1-10 GeV)
p=2
p=2.4Local Interstellar Spectrum
Aharonian 2004
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 5
Target: Interstellar Medium (Gas)Target: Interstellar Medium (Gas)• Gas distribution determined from radio surveys
velocity => distance through a rotation curveG.C.
25°
Clements(1985)(R0,v0)=(8.5 kpc, 220 km/s)
HI density from LAB surveyOpacity correction needed especially close to Gal. plane
http://www.astro.uni-bonn.de/~webaiub/english/tools_labsurvey.php
H2 density from 2.6 mm CO lineassumptions on Xco=N(H2)/WCO
Dame et al. 2001
target for producing gamma-rays through 0-decay and electron bremsstrahlung
30°
0°
-30°
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 6
Outstanding Question: Outstanding Question: EGRET GeV Excess (1)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°
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 7
Outstanding Question: Outstanding Question: EGRET GeV Excess (2)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
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 8
Intermediate Latitude Region seen by LAT (1)Intermediate Latitude Region seen by LAT (1)
|b|=10°-20°
0.1 1 10 GeV
EGRETLAT
• |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)
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 9
Intermediate Latitude Region seen by LAT (2)Intermediate Latitude Region seen by LAT (2)
0.1 1 10 GeV
EGRETLAT
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
isotropic
bremsstrahlung IC
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 10
Possible Cause of EGRET/LAT DiscrepancyPossible 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)
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 11
CR Distribution in GalaxyCR 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
OuterGalaxy
• LAT data in the 2nd and 3rd 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 2nd quadrant
• Report on the relevant study in the 3rd quadrant is in preparation
local arm
Perseus arm
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 12
Gas Density DistributionGas 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.
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 ProcedureData 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),...(),( EBEA
PS
blVBEECEblICEEG
blCOWEBblHINEAEblI
res ),()()(),,()(
),)(()(),)(()(),,(
Gamma-rays are modeled as a linear combination of each component
論文紹介 _2010-Jan.ppt
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Local HI (CR) SpectrumLocal 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
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 15
Emissivity (CR density Gradient) 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 (3rd quadrant, large-scale diffuse)
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 16
Emissivity Spectrum in Outer GalaxyEmissivity Spectrum in Outer Galaxy• HI spectral ratio to that of Gould Belt• Possible spectral hardening is observed (not seen in the 3rd quadrant)• Systematic uncertainty (unresolved sources, etc.) not ruled out
Local arm to Gould BeltPerseus arm to Gould Belt
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 17
HI vs. CO Emissivities 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)
論文紹介 _2010-Jan.ppt
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Xco EvolutionXco 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
論文紹介 _2010-Jan.ppt
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SummarySummary
• 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 2nd 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 3rd quadrant and large-scale analysis in progress
論文紹介 _2010-Jan.ppt
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HI Emissivity SpectraHI Emissivity Spectra
Gould Belt Local arm
Perseus arm
論文紹介 _2010-Jan.ppt
Tsunefumi Mizuno 21
IInternterSStellar tellar RRadiation adiation FFieldield•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 densityR=0 kpcR=4 kpcR=8 kpcR=12 kpc
CMBDustStellar
There are uncertainties associated with gas and ISRF
Porter et al. 2008