X-ray emissionfrom the gamma-ray binary LS

5039(Yamaguchi & Takahara 2012, ApJ, 761, 146 )

大阪大学　山口正輝共同研究者：　高原文郎

第 25 回理論懇シンポジウム「計算機宇宙物理学の新展開」＠つくば国際会議場　 2012/12/23

OUTLINE

I. ガンマ線連星についてII. LS 5039 とその観測III.X 線放射モデルIV. 結果V. まとめと結論

ガンマ線連星• ガンマ線が連星周期に同期して変動している連星

• AU スケールから 10TeV 以上のガンマ線が出ている！こんな天体はガンマ線連星だけ！

　　　　高密度星の近くの物理状態を調べられる　　　　 ( パルサー風やジェット )　　　　…ただ、放射機構はよくわかっていない

Objects Period

Scale Consists of …

LS 5039 3.9d 5x1012cm

O + ?? (BH or NS)

LS I +61° 303 26d 1013cm Be + ??

PSR B1259-63 3.4yr 1014cm Be + NS

HESS J0632+057 320d 1014cm Be + ??

1FGL J1018.6-5856

16d 1013cm O + ??

O star

Compact star

Observations of LS 5039A. A. Abdo, et al., 2009, ApJL, 706, 56F. Aharonian, et al., 2006, A&A, 460, 743

T. Takahashi, et al., 2009, ApJ, 697, 592

Suzaku

Fermi

HESS

・ TeV 、 GeV は反相関・ TeV 、 X 線は相関・光度は GeV で最大

Fermi

Suzaku Photon energy (eV)

Phase-averaged spectra

Orbital phase

Light curves

MS

superior

inferior

HESS

SUPC

INFC

INFCSUPC

先行研究 X 線から TeV を説明しよう

とする研究はいくつかある いずれもスペクトルまた

は周期変動に問題あり最も重要なのは…シンクロトロン冷却に よる TeV の抑制

→X 線をシンクロトロン起源としているのが問題？

T. Takahashi, et al., 2009, ApJ, 697, 592

B. Cerutti, et al., 2010, A&A, 519, 81

MSY & Takahara, 2010, ApJ, 717, 85

磁場強 TeV 小

Observations of LS 5039A. A. Abdo, et al., 2009, ApJL, 706, 56T. Takahashi, et al., 2009, ApJ, 697, 592

Suzaku

Fermi

・ X-ray と GeV がきれいに反相関している・スペクトルが滑らかにつながりそう・逆コンプトン (IC) で冷えた電子があるはず

Suzaku

Photon energy (eV)

Phase-averaged spectra

Orbital phase

Light curves

MS

superior

inferior

SUPC

INFC

INFCSUPC

Fermi

X 線は IC 放射？ ( シンクロトロンでなく )

モデル 注入電子の分布：　　　　　　べき 2.5 → IC 冷却により分布変わる　　 ( 　　　　　で決まる )

電子は高密度星の位置にいる 電子の速度は等方として入れる

電子は O 型星の光子を IC 散乱する 星由来光子の異方性考慮 電子静止系ではトムソン散乱　　 IC スペクトルを軌道位相ごとに計算

1min e

1min c

-2-3.5

)( en esccool : ttc

：フリーパラメータとするmin 41 103 ,5 c

注入率を与える → 冷却電子の数を決める

定常の電子分布

結果１（ fixed γmin ）

GeV の変動はFermi スペクトルと合うように、軌道傾斜角を調整（→ i = 15° ）

γmin = 103

GeV と X 線は同じように変動 X 線のべきが観測とよく合う (∵ 冷却電子の放

射 )

結果２（ γmin を周期変動させ fitting ）

γmin ∝ FGeV のときに X 線観測を再現できた 本質は注入率の変動で冷却電子の数が変動すること

まとめと結論

LS 5039 において、　　　　　の電子に対して IC スペクトルと光度曲線を計算し、 Suzaku の観測と比べた

スペクトルべき指数が観測と一致 γmin ∝ FGeV なら光度曲線を再現

X 線は IC で冷却した電子からの放射 X 線の変動は注入率の変動による

GeV, TeV は IC 放射で説明できる ( 我々の先行研究 ) → X 線から TeV まですべて IC 放射で説明できる

41035 e

結果

展望

星風とパルサー風 or ジェットの　 ( 磁気 ) 流体シミュレーションが必要！ 流体計算を取り入れた放射の計算はいくつか

ある (Takata et al. 2012; Zabalza et al. 2012)

これからもっと発展させていくべき！ガンマ線連星系を用いて高密度星近傍の物理に迫れる

ガンマ線連星を本当に理解するには…

star

star

議論 γmin を固定した時の変数を添え字 0 で表わす FX: X 線フラックス、 γX: X 線を出す電子の γ

GeVminGeVX,01/2-

GeVX

5.1minX,0X

1minX0X

X010

2

min

X

)1(

1

min1X

X0

XX,0X

,

5.2

)()(

)()(

)()(

)( )(

)(

FFFFF

FFp

nn

nn

nn

nFn

nFF

p

p

より

なら　

電子分布より、

∵

対立する二つの放射モデル

Microquasar model (= accretion + jet) コンパクト星は BH 星風を accretion → jet jet 内の衝撃波で粒子加速→非熱的放射

Pulsar model (= pulsar wind + stellar wind) コンパクト星は NS 二つの wind の衝突により衝撃波 そこで粒子加速→非熱的放射

star

star

Orbital parameters of LS5039

Compact star (CS) + Massive star (MS, O6.5)

Period : 3.9 days Separation　 at periastron…

~2Rstar

　 at apastron…~4Rstar

　　　　 (Rstar~ cm)Orbit of LS 5039(head on)

supc

infc

observer

periastron

apastron

MS

CS

CS

CS

CS

1210

Observations of LS 5039A. A. Abdo, et al., 2009, ApJL, 706, 56F. Aharonian, et al., 2006, A&A, 460, 743

T. Takahashi, et al., 2009, ApJ, 697, 592

Suzaku

Fermi

HESS

・ X-ray & GeV anticorrelate

Fermi

Suzaku Photon energy (eV)

Phase-averaged spectra

Orbital phase

Light curves

MS

superior

inferior

HESS

SUPC

INFC

INFCSUPC

Model (Yamaguchi & Takahara 2010) Constant and isotropic injection of electrons at CS

(power-law distribution) Cooling only by IC process → cascade Electrons emit photons at the injection or creation sites The uniform magnetic field

×: annihilation position

We calculate spectra and light curves by ① the cascade process with Monte Carlo method (GeV to TeV)②the synchrotron emission using the e± distribution for B = 0.1 G (X-ray)

→： IC photon path

MS

×

×

×

×

CS

→： MS photon path

observer

(parameters ： the inclination angle & the power-law index of injected electrons)

Electron distribution and anisotropic IC pectra

Electron energy distribution in steady state (index: 2.5)

Anisotropic IC spectra without γγ absorptionHead-

on

Rear-end

apastron

periastron

・ KN effect flattens the electron distribution・ The electron number is larger at apastron due to suppression of IC cooling

・ Anisotropic IC emission of head- on collision is more intense since collision rate is higher・ Anisotropy is suppressed by KN effect at higher energy

Comparison with observations (spectra)

Qualitative fit to observations

No fit to X-ray observations when B = 0.1G

When 3G, the best fit

Inclination angle: 30°Power-law index: 2.5

INFCSUPC

IC cascade

synchrotron__

Photon energy (eV)

0.1G

3G

Under this,synchrotron cooling isdominant

・ variation in GeV band・ ratio of TeV to GeV flux

is fitted

Comparison with observations (light curves)

TeV: roughly reproducedGeV: well reproducedX-ray: a phase difference

X

GeV

Orbital phase

Orbital phaseOrbital phase

(numerical results are normalized with maxima of observation)

TeV

Inclination angle: 30°power-law index: 2.5

Modulation mechanism in TeV, GeV and X-ray TeV: absorption is dominant At supc, flux is smaller than

infc by the large density of stellar radiation field

GeV: IC anisotropy is dominant At supc, flux is larger than

supc by head-on collision of IC scattering

X-ray: e± number variation by IC cooling

At periastron, the e± number in steady state is smaller than apastron by IC cooling in the large density of stellar radiation field, so emissivity by synchrotron is smaller, therefore flux is smaller

MSBinary axis

TeV

MS CS(inferior)CS(superior)

GeV

MS

X-ray

CS(superior) CS(inferior)

CS(apastron)CS(pariastron)

spectral break at ~1 GeV If electrons scatter off stellar photons, the

break is not reproduced Assume that the break is due to γγ

absorption Typical energy of absorbed photons: tens of

GeV

We assume that electrons scatter off 100 eV photons

0.1G

3G

GeV 30~)(~ 2massrest e,abs EEE Yamaguchi & Takahara, 2010, ApJ, 717, 85

If 10 times of thisGeV 3~absE

Therefore,

2-area model (without 100eV photon) e± are accelerated up to 1TeV and radiate in the area

(1) where B=3G e± are accelerated from 1 to 30TeV and radiate in the

area (2) where B=0.1G

We inject e± with energy,

e± with are injected in area(1) and IC photons cascade in 100eV radiation fielde± with are injected in area(2) and IC photons cascade in stellar radiation field we count the escaped photons

)cm10~( 9gyror

)~( systemgyro Lr

cm109

CS

B=3G

B=0.1G

)( cm10 system12 L

2.5) :TeV(index 50GeV 1 eETeV 1eE

TeV 1eE

Calculation method

O s

tar

Results of 2-area model without 100eV

30TeV photons are emitted and X-ray flux match obs

Problem 10GeV spectra

do not match obs As well, 10TeV

(SUPC)

Inclination angle: 30°

INFCSUPC

ーー

Model with 100eV photons

No influence on Suzaku data

Optical depth τ > 1

e± are accelerated up to 1TeV and emit near 100 eV source where B=3G

e± are accelerated from 1 to 50TeV and emit far from 100 eV source where B=0.1G

　　 we calculate cascade with 100eV photons near the source, and with stellar photons far from it

)cm10~( 9max gyro,r

)~( systemmax gyro, Lr

-134100eV s erg10L

O s

tar

cm109

CS

Requirement for 100eV source

B=3G

B=0.1G

)( cm10 system12 L

cm108100eV R

Electron injection

Results

GeV break is reproduced

But… X-ray spectra

terribly underestimate

No orbital variation in GeV & X-ray band

2.5) :TeV(index 50GeV 1 ,30 inj , eEi

Discussion

Underestimation at X-ray Energy density of 100 eV photons is larger than

that of stellar photons. → IC cooling time shorter → the number of e± smaller

No variation in GeV & X-ray band e± scatter off photons near CS→ direction to CS independent of phase→ No modulation in GeV band

The number of electrons does not change by the orbital motion→ No modulation in X-ray band

32100eVOstarOstar100eVOstar100eV 10~)(~ RRLLUU

Superior conjunction

Inferior conjunctionCS O star

CSO star

DISCUSSION 2

Underestimation at TeV TeV flux is underestimated GeV flux is overestimated We assume that 100eV photons are isotropic The flux by IC scattering is large compared

with anisotropic photon field

Anisotropic photon field

O star

Isotropic photon field

Photons through head-on collision are seen from any directionHEe± source

Spectra only with inverse Compton

Flux in the 2-area model is larger than the other →the anisotropy of target photons is important Independent of photon density and target photon

2-area model 2-area model & 1-area model

INFC

SUPC INFC

SUPC

Actually, flux of IC in the 100eV field exceed that in the stellar field

Summary For LS 5039, the break in calculated GeV spectrum

is different from that in observed one. So we introduce 100eV photon source

→ spectral break is reproduced but… X-ray flux is underestimated (by large photon

density) X-ray & GeV have no variation (by isotropy of

100eV) it is difficult to explain the high energy emission

by the model with 100 eV photons With 100eV source, we introduce orbital variation of

injection (as in Owocki et al. 2010, proceeding) Without 100eV source, we regard GeV cutoff as

high energy cutoff of injected e±