fermi 衛星でみた拡散ガンマ線放射と銀河宇宙線 tsunefumi mizuno hiroshima univ....

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


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.


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• 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)


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• 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


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°


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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°


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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


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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)


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


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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)


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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


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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.


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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


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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


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)


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


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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)


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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


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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


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HI Emissivity SpectraHI Emissivity Spectra

Gould Belt Local arm

Perseus arm


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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

fermi 衛星でみた拡散ガンマ線放射と銀河宇宙線 tsunefumi mizuno hiroshima univ....

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