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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
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 )
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±