パルサー星雲の非熱的MeVガンマ線放射

Shuta J. TanakaKonan University

128, Feb., 2017, 第一回MeVガンマ線天文学研究会@ 京都大学

Hi!

Introduction

2

PSRs & PWNe

3

Pulsar Wind Nebulae (PWNe) are powered by pulsars (PSRs)

Crab(Chandra)

Lspin I, I 1045g cm2

• Pulsed emission ~ a few % of Lspin.

=> Most of Lspin release as pulsar winds.

• ~ 70 of 2500 pulsars have observable PWNe.

• Some low Lspin pulsars also have PWNe bow shock nebulae

10-20

10-18

10-16

10-14

10-12

10-10

10-3 10-2 10-1 100 101

Perio

d D

eriv

ativ

e [s

/s]

Period [sec]

Radio PulsarsPWN detectedHigh-B Pulsars

Magnetars Pulsar wind brakes pulsar spin!

PWN & CR

4

• Confined by progenitor supernova remnant (SNR)

• Broadband emission from radio to TeV

• More efficient γ-ray emitter than SNR

• Leptonic cosmic-rays (CRs) rather than hadronic ones G21.5-0.9(Chandra)

PSRJ1833-1034

PWNG21.5-0.9

SNRG21.5-0.9

Adriani+13(AMS02)

10-6

10-5

10-4

10-3

10-2

10-1

100

1010 1015 1020 1025

Effic

ienc

y [4

π d

2 νF ν

/ L s

pin]

ν[Hz]

1E1547.0-5408Kes 75

CrabG21.5-0.9G54.1+0.3

G0.9+0.13C58

G310.6-1.6G11.2-0.3

G292.0+1.8B0540-69.3

SJ&Takahara10,11,13Tanaka16

PWN as a CR Accelerator

5

PWN Structure

6

G21.5-0.9(Chandra)

PSRJ1833-1034

PWNG21.5-0.9

SNRG21.5-0.9

Light cylinderRLC~108cm

Termination ShockRTS~ 0.1pc

ContactDiscontinuity RPWN ~ 2pc

Shock

Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ

pulsar

Magneto-sphere

Pulsar windregion

Pulsar wind nebula(shocked pulsar wind)

SN ejecta(Shocked)

SN ejecta(Unshocked)+ ISM

Crab(Chandra) Crab(HST)Crab(Composite)

Acceleration Sites

7

22 CHAPTER 3. BASIC PICTURE AND PAST STUDIES

Figure 3.2: Schematic diagram showing the co-rotating magnetosphere and the wind zone taken

from Goldreich & Julian (1969). Star is at lower left.

two distinct regions in the pulsar magnetosphere. One is the open field line region where the

plasma in this region is possible to get out from the magnetosphere along the magnetic field

line and the other, called dead zone, makes a co-rotating (see Figure 3.2). Assuming the pure

dipole magnetic field, a magnetic field line satisfies the condition r/ sin2 θ = constant. Thus

the outgoing particles are supplied from the polar cap region of the radius,

Rp ∼ RNS

!RNS

Rlc, (3.7)

where we assume RNS ≪ Rlc.

Goldreich & Julian (1969) assumed that the pulsar can supply the density of charged

particles required to fill and maintain the magnetosphere with E · B = 0. The critical density

of the charged particles required is called Goldreich-Julian density,

nGJ =ΩB

2πce, (3.8)

which is derived from E + c−1(Ω × r) × B = 0 and ∇ · E = 4πρ. The total number flux

outflowing from the polar cap region is

NGJ = 2πR2pcnGJ, (3.9)

pulsar wind

magnetosphere

?

?

?

Pulsar

Goldreich&Julian69(modified)

• PSRのパルス放射 + PWNの定常放射

• エネルギー源は同じ、PWNの方が明るい

• PSR magnetosphere = 電場加速

• PWN = 衝撃波加速 and/or 乱流加速

CrabNebula &Pulsarspectra(Buhler&Blandford14)

Spitkovsky08

SJT&Asano inprep.

Hillas Condition

8

22 CHAPTER 3. BASIC PICTURE AND PAST STUDIES

Figure 3.2: Schematic diagram showing the co-rotating magnetosphere and the wind zone taken

from Goldreich & Julian (1969). Star is at lower left.

two distinct regions in the pulsar magnetosphere. One is the open field line region where the

plasma in this region is possible to get out from the magnetosphere along the magnetic field

line and the other, called dead zone, makes a co-rotating (see Figure 3.2). Assuming the pure

dipole magnetic field, a magnetic field line satisfies the condition r/ sin2 θ = constant. Thus

the outgoing particles are supplied from the polar cap region of the radius,

Rp ∼ RNS

!RNS

Rlc, (3.7)

where we assume RNS ≪ Rlc.

Goldreich & Julian (1969) assumed that the pulsar can supply the density of charged

particles required to fill and maintain the magnetosphere with E · B = 0. The critical density

of the charged particles required is called Goldreich-Julian density,

nGJ =ΩB

2πce, (3.8)

which is derived from E + c−1(Ω × r) × B = 0 and ∇ · E = 4πρ. The total number flux

outflowing from the polar cap region is

NGJ = 2πR2pcnGJ, (3.9)

pulsar wind

magnetosphere

?

?

?

Pulsar

Goldreich&Julian69(modified)

系のサイズと磁場の大きさ => max. energy

Emax

= eBR

max

me

c2 = ecap

cap 2BNSR3NS

2c2

max

me

c2 = eB(r)r

B(r) = BNS

RNS

RLC

3 RLC

r

RLC =c

MHDを大きく破らない限り、accelerated particleの最大エネルギーはパルサー周辺のどの領域で考えても同じ

max, cap

1.3 1010

P

0.1 sec

2

B

NS

1013 G

σ-problem

9

MHDを大きく破らない限り、accelerated particleの最大エネルギーはパルサー周辺のどの領域で考えても同じ

B(r) = BNS

RNS

RLC

3 RLC

r

= 142 µG

BNS

1013 G

P

0.1 s

2 r

0.1 pc

1

磁場のエネルギーを粒子に渡しているはず!!粒子の平均エネルギーは上がるが粒子加速にはマイナス効果!!

B(rTS) = 485 µG for Crab!!

BCrab ~ 85 µG from broadband spectrumσ ~ ( BCrab / B(rTS) )2 ~ 0.031

Time-scales

10

• Acceleration time

• synchrotron cooling time

• Age of system

sketchedbyScholer

tacc

D

V 2

shock

=

3rg

vV 2

shock

0.60 yrs1

1010

B

10 µG

1

c

Vshock

2

tsyn mec2

psyn=

6mec2

TB

25 yrs

1010

1

B

10 µG

2

kyr . tage . a few 10 kyr

Maximum Energies

11

max, cap

1.3 1010

P

0.1 sec

2

B

NS

1013 G

max, cool

6.4 10101

1/2

B

10 µG

1/2 Vshock

c

max, age

1.7 10131

1

B

10 µG

Vshock

c

2

tage

1 kyr

• Hillas condition

• Size limited

• Cooling limited (tacc = tsyn)

• Age limited (tacc = tage)

1011

1012

1013

1014

1015

1016

1017

10-3 10-2 10-1 100 101

Pote

ntia

l [V]

Period [sec]

Radio PulsarsPWN detectedHigh-B Pulsars

Magnetars

max, size

1.8 109

B

10 µG

rTS

0.1 pc

Crab(Chandra)

Maximum Synchrotron Frequency

12

• Hillas condition

• Size limited

• Cooling limited (tacc = tsyn)

• Age limited (tacc = tage)

cap 8.4MeV

BNS

1013 G

2 P

0.1 sec

4 B

10 µG

2

size 161 keV

B

10 µG

3 rTS

0.1 pc

2

cool

203 MeV1

1

vshock

c

2

age

14 TeV1

2

B

10 µG

3 v

shock

c

4

tage

kyr

1

The limit written in the physical constants ~ αf

-1mec2

Too big for PWNe because vshock ~ c

Maximum Synchrotron Frequency

13

Name BPWN BMHD σPWN εsize εcapCrab 85 µG 485 µG 0.031 99 MeV 18.7 GeVG21.5-0.9 64 µG 133 µG 0.233 42 MeV 839 MeVG54.1+0.3 10 µG 76 µG 0.018 0.161 MeV 2.32 MeVKes 75 20 µG 65 µG 0.095 1.29 MeV 1.43 MeVG0.9+0.1 15 µG 150 µG 0.010 0.542 MeV 73 MeV3C58 17 µG 119 µG 0.021 0.791 MeV 47 MeVMSH15-52 17 µG 96 µG 0.031 0.791 MeV 7.2 MeVVela X 5 µG 60 µG 0.0069 0.020 MeV 1.2 MeV

rTS=0.1pcST&Takahara10, 11, 13↓cool

203 MeV1

1

vshock

c

2

One-zone Model of PWNe

14

Obs. of Max. Energy

15

Tanaka&Takahara10

Cooling limitedなら~100MeVでそうでない場合はそれ以下。~MeVの観測は大変でcut-offがちゃんと見えている天体はCrab以外にほぼない。SNRのX-rayで一応見えているけど、low-freq.過ぎるのが問題。

今回注目するところ。Crabの場合はSSCなので少し振る舞いが違うが、基本的にはcut-offは見えていない。TeV blazar で見えているのはmax. energyのcut-offではなくて、γγ-abs. でのcut-off。

Ellison+10(RXJ1713.7-3946)

Past studies

16

10-15

10-14

10-13

10-12

10-11

10-10

1010 1015 1020 1025

νFν[e

rgs/

cm2 /s

ec]

ν[Hz]

3C58 (2.5kyr)

CTA =>SYNIC/CMB

IC/IRIC/OPT

SSCTotal

10-15

10-14

10-13

10-12

10-11

10-10

10-9

1010 1015 1020 1025

νFν[ergs/cm

2 /sec]

ν[Hz]

G21.5-0.9FermiFermiFermi

SYNIC/CMBIC/IR

IC/OPTSSCTotal

10-15

10-14

10-13

10-12

10-11

10-10

10-9

1010 1015 1020 1025

νFν[ergs/cm

2 /sec]

ν[Hz]

G0.9+0.1Fermi

SYNIC/CMBIC/IR

IC/OPTSSCTotal

10-15

10-14

10-13

10-12

10-11

10-10

10-9

1010 1015 1020 1025

νFν[ergs/cm

2 /sec]

ν[Hz]

G54.1+0.3FermiFermi

SYNIC/CMBIC/IR

IC/OPTSSCTotal

SJ&Takahara11,13

Other studies

17

Abdo+10aApJ,173,416

Abdo+10bApJ,174,927

Summary

18

• PWNは潜在的にはPeV acceleratorで、パルサー磁気圏における磁力線の開き方で決まっている(old PSRも同じ)。

• パルサー風の磁場はほとんど粒子のエネルギーに変換されている(σ-problem)ため、粒子の最高エネルギーやそのシンクロトロン放射のエネルギーは小さくなる。

• Crabはsize limited, cooling limitedのエネルギーが同程度になる特殊な天体、maximum synchrotron frequencyが磁場を測るツールとして使えない。

• 他の天体ではMeV付近のsynchrotronの観測がこれまでと独立に磁場を観測する手段になり得て、σ-problemにも新しい示唆を与えることが可能。

• G21.5-0.9, 3C58くらいが狙い目だが、時間分解は必須。