Gamma-ray Opacity Mapof the Milky Way Galaxy
with CTAYoshiyuki INOUE (Kyoto)
Akira Okumura (Nagoya), Stefan Funk (SLAC)
for the CTA Collaboration

Current VHE Gamma-ray Sky
VHE ! -ray Sky Mapo+90(E!>100 GeV)

VHE ! -ray sources
Blazar (HBL)
Blazar (LBL)
Flat Spectrum Radio Quasar
Radio Galaxy
Starburst galaxy
Pulsar Wind Nebula
Supernova Remnant
Binary System
Wolf-Rayet Star
Open Cluster
Unidentifiedoo+180-180-90o

2010-10-11 - Up-to-date plot available at http://www.mpp.mpg.de/~rwagner/sources/

http://www.mppmu.mpg.de/~rwagner/sources/~60 銀河系内天体。
宇宙線加速の起源(PEVATRON)に迫りつつある。

2

Cherenkov Telescope Array (CTA) is a nextgeneration TeV Cherenkov telescope.

http://www.cta-observatory.jp/

3

CTA	  計画（チェレンコフ望遠鏡アレイ計画）
従来より一桁高い感度

1000を超えるガンマ線源が広いエネルギー領域

銀河系内・系外に発見されると予想される

Simula)on	  銀河面スキャン（HESS	  	  and	  CTA）

Gamma-ray Absorption
VHE gamma-rays are absorbed by ambient photon
field. γ(>VHE)+γ(opt-IR)→e++etypical wavelength : λ ∼ 1.24(E/TeV)µm
This leads to softening and cutoff in gamma-ray
spectra of distant sources (e.g. blazars).

Extragalactic Sources

VHE Gamma-ray Absorption
Extragalactic Background Lightblazar

IACT!VHE!EBLe+e-High redshift AGNs and GRBs enables us to study
the cosmic star formation history.

A Distant Fermi Blazar
1FGL J1344.2-1723@ z=2.49

CTA can detecta blazar at z~2.5!

50 hr, 9.03 sigma
internal MC code by Daniel Mazin

Spectrum is simply extrapolated from theFermi data (Γ=2.11).
>20 blazars at z>1.

A new probe of reionization epoch:
GeV gamma-ray attenuation
100z =0.1
z=0.1z =0.3
z=0.3z =1.0z=1.0z =3.0z=3.0

Optical Deptho DepthGamma-ray
Optical10γ(>GeV)+γUV→e++e-.
GeV flux attenuated byhigh-z UV background(Oh ’01, Gilmore+09, S.Inoue+09).

10.1
100
z=6.0z =6.0

z=5.0z =5.0z=7.0z =7.0

10

Mitaka model
Kneiske+04
S.Inoue+09

1Constraints on firststar/galaxy formation.
GRBs at z>6 by CTA ?

0.1
1

10100

1

10100

110100

Energy (GeV)
Energy[GeV]

E2 dN/dE (TeV cm-2 s-1)

GRB080916C @ z=6.5
YI EBLintrinsic spectrum, scaled by 1.000
expected spectrum (CTA), 50.00s

10-6

10-7-810

CTA can see
the PopIII signature.

10-9

10-10
0.01

0.02 0.03

0.1

0.2

0.3 0.4
1energy E(TeV)Galactic SourcesMC simulated Galactic plane map30

3 60
0-30-30-60

250 hrs
CTA-Survey in prep.

Expected Source Counts
20-70 SNRs (>3mCrab, |l|<60°, |b|<5°)
Assume 2.5 SNe/century & VHE dominant of 5 kyr300-600 PWNe (>3mCrab, |l|<60°, |b|<5°)
Assume 40 kyr lifetime
200 sources in |l|<30°, |b|<0.5° (~3 sources/deg2)
cf. ~500 AGNs are expected in the entire sky(YI, Totani, & Mori ’10, CTA-AGN in prep., CTA-Survey in prep.).

Gamma-ray Opacity of the Milky Way
Same as EBL, Galactic interstellar
radiation field (ISRF) would absorb VHE
gamma-rays (Moskalenko+’06,Zhang+’06).
Is it possible to see the PeV CR
signature with CTA, HAWC, or
LHAASO?
Is it possible to constrain the 3-D
Galactic ISRF with CTA?

IC Origin of the Galactic R

ISRF of the Galaxy1010

1! u! (µm eV cm-3 µm-1)! u! (µm eV cm-3 µm-1)

4kpc

0kpc from Galactic Center

8kpc

10-1

12kpc
10-2

10-1

110-1

10-2

1

102

10310

1! (µm)

ISRF
modelGALPROP
Fig.
1.— bySpectralenergy (Porter+’08).
distribution of the MW ISRF in the Galactic p

R = 8 kpc; magenta, R = 12 kpc. Left: maximum metallicity gradient; R
Large uncertainty
modeling.
background(CMB) isinincludedin both figures and dominates the SED for w

e.g. Cylindrical approximation for the 3-D ISRF map.

Optical Depth: Distance(l, b) = (0, 0)

11(l, b) = (0, 0)
D=1.0 kpc
=2.0 kpc=3.0 kpc=4.0 kpc=8.5 kpc=17 kpc

0.9
0.8
0.7exp(-τγγ)

Optical Depth τγγ

100.1

0.6
0.5
(l, b) = (0, 0)
0.4
0.3
0.2
0.1

0.01
0.1

110
Energy [TeV]

100

1000

00.1

D=1.0 kpc
=2.0 kpc=3.0 kpc=4.0 kpc=8.5 kpc=17 kpc

110
Energy [TeV]100

see Moskalenko+’06

Absorption is significant above 30 TeV at >4 kpc away from us.

Optical Depth : Coordinate
Distance = 8.5 kpc

11Distance : 8.5 kpc(l, b)=(0, 0)=(±30, 0)=(±60, 0)=(±90, 0)=(0, ±3)=(0, ±10)

0.9
0.8
0.7
exp(-τγγ)

Optical Depth τγγ

10

0.1

0.6
0.5
Distance : 8.5 kpc
0.4
0.3
0.2
0.1

0.01
0.1

110
Energy [TeV]

100

1000

00.1

(l, b)=(0, 0)=(±30, 0)=(±60, 0)=(±90, 0)=(0, ±3)=(0, ±10)110Energy [TeV]100

see Moskalenko+’06

E2 dN/dE (TeV cm-2 s-1)

Galactic Center @ 8.5 kpc w/ CTA (100 hr)
intrinsic spectrum 1
expected spectrum 1 (CTA), 100.00h
intrinsic spectrum 2
expected spectrum 2 (CTA), 100.00h
Crab (MAGIC)

10-11

吸収なし
10-12

吸収あり
10-13
0.01 0.02

0.1 0.2

12 3 41020
100energy E(TeV)

absorption signature at >20 TeV
it would be difficult to see >100 TeV gamma-rays
hard to see signatures of PeV CRs with distant sources

excess events

Galactic Center w/ CTA (100 hr)
Excess events, spectrum 1
Excess events, spectrum 231010210

KolmogorovSmirnovTest Probability = 3.84e-02
1Ratio in excess events

0.01

0.02

0.1

0.2 0.3

123 4 561020 30
200100Rec. energy E(TeV)

Excess events ratio
225

χ /NDF = 52.01/12, Prob = 6.18e-07

20

Chosen energy range is from 0.3 TeV to 100.0 TeV
151050.01

0.02

0.1

0.2 0.312

3 4 561020 30
200100Rec. energy E(TeV)10-11excess events

intrinsic spectrum 1
expected spectrum 1 (CTA), 100.00hintrinsic spectrum 2
expected spectrum 2 (CTA), 100.00h
Crab (MAGIC)

Excess events, spectrum 1
Excess events, spectrum 2310102

10

KolmogorovSmirnovTest Probability = 2.23e-01
10.01 0.02

0.1

0.2 0.3

123 4 56

1010-12Ratio in excess events

E2 dN/dE (TeV cm-2 s-1)

GC with H.E.S.S. (100 hr)

20 30
100 200
Rec. energy E(TeV)

Excess events ratio
1.82

χ /NDF = 6.98/11, Prob = 8.01e-01

1.6
1.4

Chosen energy range is from 0.3 TeV to 100.0 TeV

1.2
10.8

10-13
0.01 0.02

0.60.1 0.2

12 3410 20
100energy E(TeV)

0.4
0.01 0.02

0.1

0.2 0.3

123 4 561020 30
100 200
Rec. energy E(TeV)

CTA の有効面積の1/10を仮定。
H.E.S.S. クラスでは吸収の兆候を探るのは厳しい。

10-11excess events

intrinsic spectrum 1
expected spectrum 1 (CTA), 100.00h
intrinsic spectrum 2
expected spectrum 2 (CTA), 100.00h
Crab (MAGIC)

Excess events, spectrum 1
Excess events, spectrum 2
31010210

KolmogorovSmirnovTest Probability = 4.33e-01
10.01 0.02

0.1

0.2 0.3

123 4 561020 30
100 200
Rec. energy E(TeV)

10-12Ratio in excess events

E2 dN/dE (TeV cm-2 s-1)

G0.9+0.1(PWN) @ 8.5 kpc w/ CTA (100 hr)

Excess events ratio32

χ /NDF = 21.04/11, Prob = 3.30e-02
2.5
2Chosen energy range is from 0.3 TeV to 100.0 TeV

1.5
1

10-13
0.01 0.02

0.1 0.2

12 34

10 20
100energy E(TeV)

0.5
0.01 0.02

0.1

0.2 0.3

123 4 561020 30
100 200
Rec. energy E(TeV)

E2 dN/dE (TeV cm-2 s-1)

Crab @ 2kpc w/ CTA (100 hr)
intrinsic spectrum 1
expected spectrum 1 (CTA), 100.00h
intrinsic spectrum 2
expected spectrum 2 (CTA), 100.00h
Crab (MAGIC)

10-910-10

10-11

10-12

10-13

10-14
0.01 0.02

0.1 0.2

12 341020100
energy E(TeV)

Absorption would not affect nearby sources.

Future Works
1.Deabsorbed spectra catalogs ofGalactic TeV sources are required for theopacity map.
Population studies of the Galactic
sources+
2.Do created e e pairs contribute to the+Galactic e e spectrum?

Summary
CTA will detect ~300 galactic sources.
Gamma-ray absorption is significant at>4kpc above 30 TeV for CTA.
Gamma-ray opacity map would be a
key to understanding the Galactic
ISRF map.
To search PeV CRs, deep observationsof nearby sources are preferred.