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X-ray emission from 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. X-ray emission from the gamma-ray binary LS 5039. 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 連星について LS 5039 とその観測 X 線放射モデル 結果 まとめと結論. outline. 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 !

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X-ray emission from the gamma-ray binary LS 5039

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  1. (Yamaguchi & Takahara 2012, ApJ, 761, 146 ) 大阪大学 山口正輝 共同研究者: 高原文郎 X-ray emissionfrom the gamma-ray binary LS 5039 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

  2. ガンマ線連星について • LS5039とその観測 • X線放射モデル • 結果 • まとめと結論 outline

  3. ガンマ線が連星周期に同期して変動している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 ガンマ線連星 O star Compact star

  4. F. Aharonian, et al., 2006, A&A, 460, 743 A. A. Abdo, et al., 2009, ApJL, 706, 56 Observations of LS 5039 T. Takahashi, et al., 2009, ApJ, 697, 592 superior inferior Fermi HESS INFC SUPC Suzaku HESS SUPC Fermi MS INFC Suzaku Photon energy (eV) Phase-averaged spectra ・TeV、GeVは反相関 ・TeV、X線は相関 ・光度はGeVで最大 Orbital phase Light curves

  5. X線からTeVを説明しようとする研究はいくつかある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? 先行研究 T. Takahashi, et al., 2009, ApJ, 697, 592 B. Cerutti, et al., 2010, A&A, 519, 81 磁場強 TeV小 MSY & Takahara, 2010, ApJ, 717, 85

  6. A. A. Abdo, et al., 2009, ApJL, 706, 56 Observations of LS 5039 superior inferior T. Takahashi, et al., 2009, ApJ, 697, 592 Fermi Fermi INFC SUPC Suzaku Suzaku SUPC MS INFC Photon energy (eV) Orbital phase Phase-averaged spectra Light curves ・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 X線はIC放射?(シンクロトロンでなく)

  7. 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 モデル 定常の電子分布 -2 -3.5 :フリーパラメータとする 注入率を与える → 冷却電子の数を決める

  8. 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1(fixed γmin)

  9. 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 結果2( γmin を周期変動させfitting)

  10. 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 まとめと結論 結果

  11. 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 展望 star star ガンマ線連星を本当に理解するには…

  12. 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 議論

  13. 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 対立する二つの放射モデル star star

  14. Compact star(CS) + Massive star (MS, O6.5) Period : 3.9 days Separation at periastron…~2Rstar at apastron…~4Rstar (Rstar~cm) Orbital parameters of LS5039 supc CS periastron CS MS apastron CS infc CS observer Orbit of LS 5039(head on)

  15. F. Aharonian, et al., 2006, A&A, 460, 743 A. A. Abdo, et al., 2009, ApJL, 706, 56 Observations of LS 5039 T. Takahashi, et al., 2009, ApJ, 697, 592 superior inferior Fermi HESS INFC SUPC Suzaku HESS SUPC Fermi MS INFC Suzaku Photon energy (eV) Phase-averaged spectra ・X-ray& GeVanticorrelate Orbital phase Light curves

  16. Model (yamaguchi& Takahara 2010) • Constant and isotropic injection of electrons at CS (power-law distribution) • Cooling only by IC process → cascade • Electrons emit photonsat the injection or creation sites • The uniform magnetic field observer × × × MS CS × We calculate spectra and light curves by ① the cascade processwith Monte Carlo method (GeVto TeV) ②the synchrotron emission using the e± distribution for B = 0.1 G (X-ray) ×: annihilation position →:ICphoton path →:MSphoton path (parameters: the inclination angle & the power-law index of injected electrons)

  17. Electron distribution and anisotropic IC pectra Electron energy distribution in steady state (index: 2.5) Anisotropic IC spectra without γγ absorption Head-on apastron Rear-end 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

  18. Comparison with observations (spectra) ・variation in GeV band ・ratio of TeV to GeV flux Inclination angle: 30° Power-law index: 2.5 • Qualitative fit to observations • No fit to X-ray observations when B = 0.1G • When 3G, the best fit is fitted _ _ INFC synchrotron SUPC 3G 0.1G IC cascade Under this, synchrotron cooling is dominant Photon energy (eV)

  19. Comparison with observations (light curves) Inclination angle: 30° power-law index: 2.5 TeV X Orbital phase Orbital phase GeV TeV: roughly reproduced GeV: well reproduced X-ray: a phase difference Orbital phase (numerical results are normalized with maxima of observation)

  20. 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, thee± 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 Modulation mechanism in TeV, GeV and X-ray TeV Binary axis MS CS(superior) CS(inferior) GeV MS CS(superior) CS(inferior) X-ray CS(apastron) MS CS(pariastron)

  21. 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 spectral break at ~1 GeV Yamaguchi & Takahara, 2010, ApJ, 717, 85 3G If 10 times of this Therefore, 0.1G

  22. e±are accelerated up to 1TeVand 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 field e± with are injected in area(2) and IC photons cascade in stellar radiation field we count the escaped photons 2-area model (without 100eV photon) Calculation method B=0.1G B=3G O star CS

  23. 30TeV photons are emitted and X-ray flux match obs Problem 10GeVspectra do not match obs As well, 10TeV (SUPC) Results of 2-area model without 100eV Inclination angle: 30° ー ー INFC SUPC

  24. No influence on Suzaku data Optical depth τ> 1 e± are accelerated up to 1TeVand 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 Model with 100eV photons Requirement for 100eV source B=0.1G B=3G O star CS Electron injection

  25. GeV break is reproduced But… X-ray spectra terribly underestimate No orbital variation in GeV & X-ray band Results

  26. Underestimation at X-ray • Energy density of 100 eV photons is larger than that of stellarphotons. → IC cooling time shorter → the number of e± smaller No variation in GeV & X-ray band • e± scatter offphotonsnear 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 Discussion Superior conjunction O star CS Inferior conjunction O star CS

  27. Underestimation at TeV TeV flux is underestimated GeVflux is overestimated We assume that 100eV photons are isotropic The flux by IC scattering is large compared with anisotropic photon field Discussion 2 Anisotropic photon field Isotropic photon field Photons through head- on collision are seen from any direction O star HEe±source

  28. 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 Spectra only with inverse Compton Actually, flux of IC in the 100eV field exceed that in the stellar field 2-area model & 1-area model 2-area model SUPC SUPC INFC INFC

  29. 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± Summary

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