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
Fermi_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
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_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
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 11
Fermi_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
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
Fermi_Diffuse_ASJ_2009Sep.ppt
HI MapsHI Maps
R<=10 kpc
R<=12.5-16 kpc
R<=10-12.5 kpc
R>=16 kpc