Fermi_Diffuse_ASJ_2010Mar.ppt
Fermi-LAT Study of
Galactic Cosmic-Ray
Distribution
-- CRs in the Outer Galaxy --
Tsunefumi Mizuno
Hiroshima Univ.
on behalf of the Fermi-LAT
Collaboration
ASJ 2010 Spring Meeting
March 25, 2010, Hiroshima, Japan
Tsunefumi Mizuno
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Introduction
Fermi_Diffuse_ASJ_2010Mar.ppt
Cosmic-Rays and Galactic Diffuse Gamma-Rays
HE g-rays are produced via interactions between cosmic-rays (CRs)
and the interstellar medium (or the interstellar radiation field)
Fermi-LAT (2008-present)
2.4p sr, 30 MeV-300 GeV
• ISM distribution => CRs
• those “measured” CRs => ISM
A powerful probe to study CRs and ISM in distant locations
Tsunefumi Mizuno
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Fermi_Diffuse_ASJ_2010Mar.ppt
LAT Study of the Galactic Diffuse Emission
[1]: CR sources: SNRs, HESS unIDs (Katagiri et al., Hanabata et al.)
[2]: ISM and possible CR sources: molecular clouds (Okumura et al., Sada et al.)
Fermi-LAT all sky map (1yr)
[3]: Galactic CRs: This talk (cf. Abdo et al. 2009, ApJ 703, 1249; Abdo et al.
2009, PL 103, 251101; Abdo et al. 2010, ApJ 710, 133)
Tsunefumi Mizuno
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Fermi_Diffuse_ASJ_2010Mar.ppt
CR Distribution in Milky Way
• CR distribution is a key to
understand the CR origin and
propagation
Gal.
Center
Inner Galaxy
Outer
Galaxy
Tsunefumi Mizuno
• ISM gas distribution is traced
by radio surveys + Galactic
rotation
• Then, Fermi-LAT is able to
map out CR distributions in
Milky Way with unprecedented
accuracy
• Detailed study of the outer
Galaxy (2nd and 3rd quadrant)
will be discussed.
• Study of the whole Galaxy is
in progress
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Fermi_Diffuse_ASJ_2010Mar.ppt
CR Distribution in the Outer Galaxy
(2nd Quadrant)
• CR distribution is a key to
understand the CR origin and
propagation
Gal.
Center
Inner Galaxy
• ISM gas distribution is traced
by radio surveys + Galactic
rotation
• Then, Fermi-LAT is able to
map out CR distributions in
Milky Way with unprecedented
accuracy
Gould Belt
Outer
Galaxy
Abdo et al. 2010 (ApJ 710, 133)
Contact: L. Tibaldo, I. Grenier
Tsunefumi Mizuno
R=8.8 kpc
local arm
R=10 kpc
Perseus arm
outer arm
R=14 kpc
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Fermi_Diffuse_ASJ_2010Mar.ppt
CR Distribution in 2nd Quadrant
g-ray emissivity (per H-atom)
• The shape of CR spectrum in Gould
Belt (d<=300 pc) is close to those
measured at the Earth
pion-dacay
model (scaled)
Bremsstrahlung
200 MeV
g-ray intensity profile
GALPROP prediction
• Decrease of CR densities with
gradient flatter than expectations for
SNR sources as traced by PSR
using PSR distribution as
input sources
Fermi data
• Property of molecular clouds is also
discussed in paper
Tsunefumi Mizuno
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Fermi_Diffuse_ASJ_2010Mar.ppt
CR Distribution in the Outer Galaxy
(3rd Quadrant)
• CR distribution is a key to
understand the CR origin and
propagation
Gal.
Center
Inner Galaxy
• ISM gas distribution is traced
by radio surveys + Galactic
rotation
• Then, Fermi-LAT is able to
map out CR distributions in
Milky Way with unprecedented
accuracy
outer arm
Outer
Galaxy
Perseus arm
inter arm
R=16 kpc
R=12.5 kpc
R=10 kpc
local arm
Tsunefumi Mizuno
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Fermi_Diffuse_ASJ_2010Mar.ppt
CR Distribution in 3rd Quadrant
g-ray emissivity (per H-atom)
• Spectral shape agrees well with the
model for the LIS, and no significant
spectral shape variation is observed.
• CR spectrum in Tp~1-100 GeV does
not vary significantly in the region
studied
g-ray intensity profile
• Consistent view of CR density
gradient: Decrease of CR densities
with gradient flatter than expectations
by a conventional model
Tsunefumi Mizuno
Fermi data
GALPROP
prediction
using SNR distribution
(Case & Bhattacharya 1998)
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Fermi_Diffuse_ASJ_2010Mar.ppt
Possible Scenario of CR Density
Distribution
• We ran GALPROP to search a possible scenario to explain the flat CR density
distribution obtained by the LAT
 Large halo size is required to reproduce the LAT data
 Or, a flat source distribution in the outer Galaxy is required
test of several
halo sizes
Zh = 1, 2, 4,
10, 15, 20 kpc
test of a flat CR source
distribution in R>Rbk
Rbk = 10, 11, 12,
13, 14, 15 kpc
• A larger halo size and/or a flatter CR source distribution than
those by a conventional models are required
• Other scenarios may also explain the observed profile (e.g., Evoli
et al. 2008)
Tsunefumi Mizuno
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Fermi_Diffuse_ASJ_2010Mar.ppt
Summary
• 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
 CR sources (Katagiri et al., Hanabata et al.)
 individual GMCs (Okumura et al., Sada et al.)
 non-GeV-excess, mid/high-latitude region (local CRs)
 large scale analysis (CR distribution throughout the
Galaxy)
• Detailed study of the outer Galaxy is discussed
 Flatter CR density gradient than a conventional model
toward the outer Galaxy
 Flat CR source distribution and/or a large CR halo is a
possible scenario
Thank you for your attention!
Tsunefumi Mizuno
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Fermi_Diffuse_ASJ_2010Mar.ppt
Backup Slides
Tsunefumi Mizuno
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Fermi_Diffuse_ASJ_2010Mar.ppt
CR Distribution in 3rd Quadrant
• Spectral shape agrees well with the model for the LIS, and no significant
spectral shape variation is observed.
• CR spectrum in Tp~1-100 GeV does not vary significantly in the region studied
Tsunefumi Mizuno
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Fermi_Diffuse_ASJ_2010Mar.ppt
Fermi-LAT View of the 3rd Quadrant
• One of the best studied regions in g-rays
 Vela, Geminga, Crab and Orion A/B
• Galactic plane between Vela and Geminga (green square) is ideal to study diffuse g-rays
and CRs.
 small point source contamination, kinematically well-separated arms (local arm
and Perseus arm)
Geminga
Vela
Crab
Orion A/B
Tsunefumi Mizuno
Count Map (E>100 MeV)
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Fermi_Diffuse_ASJ_2010Mar.ppt
Construction of the Model
Local arm
Perseus arm
+
Local arm
+2 HI maps
(profile fitting technique;
arXiv:0907.0312)
• Fit g-ray data with 8 maps
+ 15 point sources (11
month source list)
• CR spectrum (g-ray
emissivity) is assumed to
be uniform in each
Galactocentric ring
+ 1 CO map + excess E(B-V) map (Grenier et al. 2005)
+ IC map (galprop model) + point sources (11 month list)
Tsunefumi Mizuno
I(E, l, b) = SA(E)*HI(l,b) + SB(E)*Wco(l,b)
+Sothers+Spoint_sources
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Introduction
Fermi_Diffuse_ASJ_2010Mar.ppt
Cosmic-Rays and Galactic Diffuse Gamma-Rays
HE g-rays are produced via interactions between Galactic cosmic-rays
(CRs) and the interstellar medium (or interstellar radiation field)
(CR accelerator)
SNR
RX J1713-3946
(Interstellar space)
X,γ
(Observer)
ISM
+
e-
Chandra, Suzaku,
Radio telescopes
B
HESS
Pulsar,
m-QSO
P diffusion
He
energy losses
CNO
reacceleration +
convection e
+
etc. π -
(GMC is one of the best
target matter)
gas
IC
ISRF
gas
π0
ACTs and Fermi
(see K. Hayashi’s talk)
Pioneering theoretical works by Hayakawa (1952), Morrison (1958), etc.
A powerful probe to study CRs and ISM in distant locations
Tsunefumi Mizuno
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