fermi-lat study of galactic cosmic-rays by observing diffuse gamma-rays

Tsunefumi Mizuno 1

Fermi_Diffuse_ASJ_2009Sep.ppt

Fermi-LAT Study of Fermi-LAT Study of Galactic Cosmic-Rays Galactic Cosmic-Rays by Observing Diffuse by Observing Diffuse

Gamma-raysGamma-rays(Fermi(Fermi 衛星による拡散衛星による拡散γγ 線放射の観測と銀河線放射の観測と銀河

系宇宙線系宇宙線 ))Tsunefumi MizunoTsunefumi Mizuno

Hiroshima Univ.Hiroshima Univ.on behalf of the Fermi-LAT on behalf of the Fermi-LAT

CollaborationCollaborationASJ 2009 Autumn MeetingASJ 2009 Autumn Meeting

September 15, 2009, Yamaguchi, JapanSeptember 15, 2009, Yamaguchi, Japan

Tsunefumi Mizuno 2

Fermi_Diffuse_ASJ_2009Sep.pptIntroduction Introduction 銀河宇宙線と拡散銀河宇宙線と拡散 γγ 線放射線放射

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.

拡散 γ 線は宇宙線を探るプローブ

Tsunefumi Mizuno 3


FermiFermi 衛星による拡散衛星による拡散 γγ 線放射の観測線放射の観測 (1)(1)

[1]: GMCs (e.g., Orion, Cham): matter distribution, correlation with mol. gas tracer [2]: Mid/low-latitude region (EGRET GeV excess). submitted to PRL. See also ArXiv:0907.0294

[3]: Mid/high-latitude region to study local CRs. (Abdo et al. 2009; contact: T. Mizuno) [4]: Galactic plane (CR distribution in the MW)

[1]~[3] について、これまでの結果を簡単に紹介 ( 次項 )[4] について若干詳しく

Tsunefumi Mizuno 4


FermiFermi 衛星による拡散衛星による拡散 γγ 線放射の観測線放射の観測 (2)(2)

electron-bremsstrahlung

nucleon-nucleon

LAT datamodel for the LIS

0.1 1 10 GeV

EGRETLAT

Preliminary

Preliminary

Orion MC(M~105Msun)

Cham MC(M~104Msun)

Preliminary

Preliminary

[1]:GMCs物質分布

[2]: non-GeV-excessGeV-excess の否定

[3]: local CRs近傍の宇宙線は LIS に酷似

Tsunefumi Mizuno 5


銀河系内の宇宙線分布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)

Gal.Center

Inner Galaxy

OuterGalaxy

• 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)

local arm

Perseus arm

宇宙線の空間分布は、起源・伝播を探る鍵

銀河系の外側の領域の結果の紹介

Tsunefumi Mizuno 6


Fermi-LATFermi-LAT のカウントマップのカウントマップ• One of the best studied regions in -rays

Vela, Geminga, Crab and Orion A/B• Galactic plane between Vela and Geminga (green square) is ideal to study diffuse -rays and CRs.

small point source contamination, kinematically well-separated arms (local arm and Perseus arm)

Count Map (E>100 MeV)

Preliminary

Preliminary

Vela

Crab

Geminga

Orion A/B

宇宙線分布の研究に適した領域

Tsunefumi Mizuno 7


線線 = = 星間物質からの放射星間物質からの放射 ++ 点源点源Local arm

+2 HI maps(profile fitting technique;

arXiv:0907.0312)

+

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) = A(E)*HI(l,b) + B(E)*Wco(l,b) +others+point_sources

Preliminary

Preliminary

Perseus arm

• Fit -ray data with 8 maps + 15 point sources (11 month source list)• CR spectrum (-ray emissivity) is assumed to be uniform in each Galactocentric ring

詳細は林の講演参照 (Q28a)

Tsunefumi Mizuno 8

Fermi_Diffuse_ASJ_2009Sep.ppt 線スペクトル線スペクトル (~(~ 宇宙線スペクト宇宙線スペクトルル ))

Preliminary

Preliminary

HI Emissivity Spectrum of each ring

Point sources with Ts>=100 are included in the fitting

(local arm)(interarm)(Perseus arm)

• 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

宇宙線陽子で 1-100GeV に対応 ( 主成分 )

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

Tsunefumi Mizuno 9


SummarySummary

Thank you for your attention!

• 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

Tsunefumi Mizuno 10


Backup SlidesBackup Slides

Tsunefumi Mizuno 11


LAT vs pre-Fermi ModelLAT vs pre-Fermi Model

Preliminary

Preliminary

• 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

The model is successful considering it is a priori

pre-Fermi model

LATmodel total

0-decay

ICe-Brems

Tsunefumi Mizuno 12


Probing CRs using Gamma-rays from ISMProbing 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

ISM(e.g., LAB HI survey)

(http://www.astro.uni-bonn.de/~webaiub/english/tools_labsurvey.php)

Gamma-ray intensity(Fermi LAT data)

Mid/high latitude region & Galactic plane:Study of the local CRs and CR gradient in the outer Galaxy

GCsun

(From Wikipedia)

Tsunefumi Mizuno 13


Accurate Measurements of Local CRs (1)Accurate Measurements of Local CRs (1)

Mid-high lat. region in 3rd quadrant:• small contamination of IC and molecular gas• correlate -ray intensity and HI gas column density

Abdo et al. 2009, accepeted by ApJ(arXiv:0908.1171) contact author: TM

400-566 MeV

HI column density (1020 cm-2)

(error bars are statistical only)

E2 x

-r

ay

Inte

ns

ity

HI column density (1020 cm-2)

1.6-2.3 GeV400-560 MeV

Tsunefumi Mizuno 14


Accurate Measurement of Local CRs (2)Accurate Measurement of Local CRs (2)• Best quality -ray emissivity spectrum in 100 MeV-10 GeV (Tp = 1-100 GeV)• Agree with the model prediction from the local interstellar spectrum (LIS)

• Prove that local CR nuclei spectra are close to those directly measured at the Earth• E<100 MeV constrain the e- spectrum

102 103 MeV 104

EGRET (Digel et al. 2001)

electron-bremsstrahlung

nucleon-nucleon

LAT datamodel from the LIS

Tsunefumi Mizuno 15


CR Flux DistributionCR Flux Distribution

• 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.

Preliminary

Preliminary

LAT “measured” CR density

SNR distribution by radio survey or traced by pulsar

Tsunefumi Mizuno 16


HI MapsHI Maps

R<=10 kpc

R<=12.5-16 kpc

R<=10-12.5 kpc

R>=16 kpc

Tsunefumi Mizuno 17


Wco MapsWco Maps

R<=10 kpc R<=10-12.5 kpc

fermi-lat study of galactic cosmic-rays by observing diffuse gamma-rays

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