Interstellar Medium
in the Middle-aged SNRs
Satoshi Yoshiike
Nagoya University

The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)

SNR: Origin of Galactic CRs ?
† Observe γ-ray produced by hadronic process‡ p(CR) + p(ISM)  π0 + … , π0  2γ
† Two approaches:

The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)2

SNR: Origin of Galactic CRs ?
† Observe γ-ray produced by hadronic process‡ p(CR) + p(ISM)  π0 + … , π0  2γ
† Two approaches:age ~ 10,000 yr
age ~ 1,000 yr

age < 1,000 yr
1 GeV

1 TeV

Funk ‘15

1. Characteristic spectral break† Direct evidence† Useful for middle-aged SNRs
† NO information about ISM proton
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)3

SNR: Origin of Galactic CRs ?
† Observe γ-ray produced by hadronic process‡ p(CR) + p(ISM)  π0 + … , π0  2γ
† Two approaches:age ~ 10,000 yr
age ~ 1,000 yr

Image：ISM protons（H2+HI）
Contours ：TeV γ-rayage < 1,000 yr
RX J1713.7-3946
1 GeV

1 TeVFunk ‘15

Fukui+ ’12

1. Characteristic spectral break
2. Spatial correlation: ISM proton and γ† Direct evidence† Useful for young TeV γ-rays† Useful for middle-aged SNRs
† Available mass of ISM proton† NO information about ISM proton‡ enable to estimate Wp
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)4

SNR: Origin of Galactic CRs ?
† Observe γ-ray produced by hadronic process‡ p(CR) + p(ISM)  π0 + … , π0  2γ
† Two approaches:age ~ 10,000 yr
age ~ 1,000 yr

Image：ISM protons（H2+HI）
Contours ：TeV γ-ray

It is important to show both:
spectral break and existence of target protons
age < 1,000 yr
RX J1713.7-3946
1 GeV

1 TeV

Funk ‘15

Fukui+ ’12

1. Characteristic spectral break
2. Spatial correlation: ISM proton and γ† Direct evidence† Useful for young TeV γ-rays† Useful for middle-aged SNRs
† Available mass of ISM proton† NO information about ISM proton‡ enable to estimate Wp
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)5

Middle-aged SNRs: W44, IC 443
W44

Image: GeV γ-ray (Fermi-LAT)
Contours: 1.4 GHz conti. (VLA)IC443

Image: TeV γ-ray (VERITAS)
Contours: 1.4 GHz conti.
(DRAO Synthesis Telescope)† Spectral break was confirmed by AGILE and Fermi-LAT
Giuliani+ ’11, Ackermann+ ’13† This work: Analyzed ISM (CO, HI, Dust) data to identify the target
protons for the hadronic γ–rays.
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)

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NANTEN2 telescope− Location: Chile, Atacama (alt. 4,850m)− Frequencies: 100 GHz: CO(J = 1–0)
HPBW ~ 2.7’
 ~ 2.3 pc (at W44)
 ~ 1.1 pc (at IC 443)
 200 GHz: CO(J = 2–1)
HPBW ~ 1.5’
 ~ 1.3 pc (at W44)
 ~ 0.65 pc (at IC 443)
− Advantages
 Moderate beam size
Good for observing large area and/or many objects.
 Multi-line observation
Investigate for physical properties of ISM
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)7W44: Yoshiike et al. 2013
†Large scale distribution of 12CO(J=1–0) by NANTEN‡ W44 is embedded in “Molecular Ridge”.

W44+:YSO candidates

The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)8

W44: Yoshiike et al. 2013†

Velocity Channel Map of 12CO(J=2–1): 30 - 60 km/s, 5 km/s interval‡ V = 40 – 50 km/s : GMC is located at Eastern-side‡ V = 50 – 60 km/s : Clouds surround the shellN

Contours: 1.4 GHz conti. (VLA)The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)9

W44: Yoshiike et al. 2013
†Velocity Channel Map of 12CO(J=2–1): 30 - 60 km/s, 5 km/s interval‡ V = 35 – 45 km/s : Candidate of the target protons

N

Contours: GeV γ-ray (Fermi-LAT)
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)10

W44: Yoshiike et al. 2013
† Distribution of ISM proton column density
Molecular H [×1021 cm-2]

Atomic H [×1020 cm-2]+Total H [×1021 cm-2]=† Target protons are dominated by molecular gas: n(H2):n(HI) ~ 10 : 1‡ different situation from young SNRs: n(H2):n(HI) ~ (0–1) : 1† np ~ 200 cm-3, Wp ~ 1049 erg (~ 1 % × ESN)
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)11

IC 443: Molecular Gas Distribution† Narrow component: -3 km/s clouds† Clumps: (Blue) -18 – -6 km/s, (Red) 0 – +10 km/s
‡ Broad wings + High intensity ratio of CO 2–1/1–0
 Interaction with SNR shock-3km/s cloud

CO(J=2–1)
CO(J=1–0)

Radio Shell
Green: CO 1–0
Blue, Red: CO 2–1

The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)12

IC 443: Gas Location relative to the SNR† Spatial Comparison: Soft X-ray (0.4–0. 75 keV) vs CO (J=1–0)† X-ray shows anti-correlation with -3km/s cloud‡ -3km/s clouds is located in front of IC443

Image：XMM-Newton
Contours：CO(J=1–0)
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)13τ353: Tracer of Hydrogen† Dust opacity at 353 GHz, τ353 （Planck/IRAS）‡ τ353 ≲ 10-3, δτ353/τ353 ≲ 10 %‡ Good tracer of interstellar hydrogen
Fukui+ ’14 (MBM 53, 54, 55 + HLCG 92-35), ‘15 (All-sky), ’17 (MHD simulation)

δτ353/τ353

τ353

 8%

 10-3

Planck Collaboration+ ‘14† Okamoto+ ‘17 derived the relation between NH and τ353
in the Perseus clouds.

The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)14τ353: Tracer of Hydrogen† CO and τ353: similar spatial distributions† HI: a low contrast and more extended distribution
 Corresponds to a diffuse part of τ353.
τ353 is useful as the tracer of H in IC 443 region !
CO(1–0) Integrated Intensity

HI Integrated Intensity

Dust opacity at 353 GHzRadio Shell

The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)15

X-factor (XCO) in IC 443† X-factor: XCO (≡ N(H2) / WCO)
‡ Typical value in the Galaxy: (1–3)

1020 cm-2/(K km/s)
e.g., see Bolatto+ ’13, Table 1† Total H column density from τ353 Okamoto+ ’17‡ NH = (9.0 1024) τ3531/1.3 (cm-2)
 H2 column density

N(H2) = XCOWCO

 Total H column density

NH = 2

N(H2) + N(HI)NH [× 1022 cm-2]† XCO in IC 443~10 % NH = (2 × XCO) × WCO + N(HI)XCO = Slope/2= 1.21020 cm-2/(K km/s)

WCO [K km/s]
Using points with WCO > 3σ in Shell

The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)16

IC 443: Target Protons and CR Proton Energy† Good correspondence between
molecular cloud and γ-ray peaks† Mass: 580 M8 / Size ~ 4pc‡ np: 680 cm-3
† γ-ray Flux (0.1 – 100 GeV)
‡ Fγ = 502.1×10-12 erg cm-2 s-1
Fermi LAT 3rd Source Catalog (Acero+ ‘15)

† Total CR Proton Energy‡ Wp ~ 9×1047 (np/680 cm-3)-1 erg
cf. Ackermann+ ’13
Wp ~ 4 1049 (np/20 cm-3)-1 erg

Image: TeV γ-ray (VERITAS)
Contours
White：CO(J=1–0) (-18 – +2 km/s)
Red：1.4 GHz radio conti.
(DRAO Synthesis Telescope)

The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)17

Energy Budget for CRs
Efficiency of CR acceleration† Wp ~ 9×1047 erg‡ 0.1 % of ESN⇔ 1 – 10 % is required† NON-uniform proton distribution‡ γ-rays reflect only a part of total
CR protons.

Image: TeV γ-ray (VERITAS)
Contours
White：CO(J=1–0) (-18 – +2 km/s)
Red：1.4 GHz radio conti.
(DRAO Synthesis Telescope)
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)18

Energy Budget for CRs
Efficiency of CR acceleration† Wp ~ 9×1047 erg‡ 0.1 % of ESN⇔ 1 – 10 % is required† NON-uniform proton distribution‡ γ-rays reflect only a part of total
CR protons.
† Escape of CRs from SNR

WescW44

W28(0.3—3) × 1050 erg> 2 × 1049 erg

W44; Uchiyama+ ‘12, W28; Hanabata+ ‘14† True Wp could archive 1 – 10 % of ESN† CR energy of this work provides
reasonable lower limit.

Image：CO(J=1-0) (NANTEN2)
Contours
red： GeV γ-ray (Fermi-LAT)
White：1.4 GHz cont. (VLA)The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)19Contribution of Molecular and Atomic Proton† Analysis of W44, IC443 (, and W28)
‡ Molecular gas is a major target in middle-aged SNRs.
‡ H2 : HI ~ 10 : 1† Young SNRs show different trend:
RX J1713.7-3946

RX J0852.0-4622

HESS J1731-347

RCW 86Age (yr)

1,000

1,700

4,000

1,800

M(H2):M(HI)1:1

0.1 : 1

4:1

0:1

RX J1713.7-3946; Fukui et al. (2012), RX J0852.0-4622; Fukui (2013), Fukui et al. (2017)
HESS J1731-347; Fukuda et al. (2014), RCW86; Sano et al. in prep† Is this a universal trend ? , What makes this difference ?
‡ More samples (Age, Type, surrounding)- Galactic and also Magellanic SNRs.
‡ MHD simulation of shock propagation into ISM for t ~ 104 yr
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)20

Conclusion† W44 and IC443 actually have target protons for hadronic γ–rays.
† Determined the XCO more accurately for IC 443 using dust data.
† Wp ~ 1048 – 1049 erg, 0.1 – 1 % of ESN• Low efficiency can be explained by the non-uniform distribution of thetarget protons and escape of CRs.
• γ–ray observation not only toward SNR but also its surroundings isimportant.

† Target protons tend to be dominated by H2 in Middle-aged SNRs.
• Increase samples using large-scale Galactic CO survey data:- COHRS: JCMT 15m Dempsy+ ‘13- The Mopra Galactic Plane CO Survey: Mopra 22m- NASCO: NANTEN2 4m- FUGIN: Nobeyama 45m Umemoto+ ‘17
The extreme Universe viewed in very-high-energy gamma rays 2017 (Dec. 18 – 19, 2017)21