特別推進研究研究会・宇宙線研究所共同利用研究会「高エネルギーガンマ線でみる極限宇宙2013」 2013年9月4日(火)東京大学柏キャンパスNANTEN2とSuzaku衛星による若いTeVガンマ線SNRの研究佐野栄俊（Hidetoshi SANO;名大理D3）共同研究者: 福田達哉,吉池智史,鳥居和史,早川貴敬,山本宏昭,立原研悟,犬塚修一郎,福井康雄(名大理),田中孝明(京大理),松本浩典(名大KMI),内山泰伸(立教大理),井上剛志,山崎了(青山学院大理),河村晶子,水野範和(NAOJ),水野亮(名大STE),西村淳,大西利和(大阪府立大理), 他NANTENチーム
SNRにおける Cosmic-Rays (CRs)の加速は,ほぼ揺るぎないものに(e.g., Fermi results) ■ →しかし,本当にKnee energy付近までCRsは加速されているのか？若く(~2000yr) TeVガンマ線で明るいSNRが,現段階ではこの鍵を握る最有力ターゲット"年齢2000年程度の4つのTeVガンマ線SNRs ■ →どの天体もISM (Interstellar Medium)との相互作用が確認視直径: ~1 deg. ~2 deg. ~1700–4300 yr rich Hı + little CO rich CO + Hi cavity rich Hı + little CO pure synchrotron ? thermal + non-thermal pure synchrotronこれらの高エネルギー放射起源や効率の良いCRs加速と, ISMが密接に関係■ ~0.5 deg. ~0.5 deg.年齢:  ~1600 yr ~3600–7200 yr ~1800 yr ISM:  rich CO + cold Hı X-rays: pure synchrotron
RXJ1713, Vela Jr. HESSJ1731のTeV γ線とISMの相関Total energy in accelerated protons ..... Target ISM proton density .... Distance to the SNR図1 :宇宙線起源の高エネルギー放射模式図↑ e.g., RXJ1713 (Fukui, Sano et al. 2012)高度に非一様なISM分布CRs protonの加速効率は~0.1 % (~1048 erg)しかしながら,この空間分解能で議論できるのは視直径の大きなSNRに限られる. ■ → CTA時代まで待つか、いま我々が他にできることは? ■ SNR shock wavesとISMの相互作用(Shock-cloud interaction) ⇒ ISM clump周辺で乱流励起+磁場増幅⇒観測的にはclump周辺のX線増光として確認できる高空間分解能/高統計のX線データ +  SNRと相互作用する ISM CR electron accelerationについての知見を深める
TeVガンマ線SNRの中でも最も重要なターゲットの1つ■ ⇒ Rich CO + Cold Hiとの相互作用, Pure Synchrotron X-rays,視直径~1 deg. NANTEN2 CO ……… HPBW ~1.5−3 arcmin Suzaku X-rays ……… HPD ~2 arcmin ATCA & Parkes H ı ….. HPBW ~2.2 arcmin Sano+13a arXiv: 1304.7722 images:  Suzaku 1–5 keV mosaics,  contours: ¹²CO(J=2–1) integrated intensity (two velocity ranges)
◾ 17 clumps全てで, COとX-rayのanti-correlationがみえている
Solid boxes: source regions Dashed boxes: background regions Typical X-ray spectraノand best fit parameters →
Source grid size 2'−8',計315領域からスペクトルを抽出(FI CCDs only). ■ → Absorbing column density N H (X-ray)のrelativistic error < 30 ％となるように調整Absorbed power-low modelでfitting (at least ~100 counts / bin). ■ Sano+13b in prep.
️Maps of the Best-fit parameters (a) absorbing column NH(X-ray) (b) photon index Γ (c) absorption-corrected X-ray flux (3−10 keV) (contours indicate the smoothed XIS 1–5 keV image) ○ Relative error (90% confidence level) NH(X-ray)… ~14 % (max 30%) Г …………. ~6 % (max 13%) Flux………. ~7 % (max 23%)
^↑Maps of NH(X-ray) and visual extinction (Dobashi+05) ← Correlation plot - correlation coefficient: ~0.83 - NH(X-rays) (cm-²) = 3.0×10²¹ • Av (mag.) cf. N H (cm¯²) = 2.5×10²¹ • Av (mag.) (Jenkins & Savage+74) NH(X-rays) ~0.4–1.4×10 22 cm -2の範囲で変化→ Cassam-Chenai+04の傾向とconsistent NH(X-rays)とVisual Extinctionの非常に良い相関
○ Foreground component NH, local(H2+H1) is identified by Moriguchi+05 with NANTEN and ROSAT data. ○ ISM proton column density estimation □ NH (H 2 +HI) = 2×N(H 2 ) + NH (HI). □ N(H 2 ) (cm −2 ) = Xco (cm −2 (K km s −1 ) −1 ) ×W(CO) (K km s−1). □ Xco = 2 × 10 20 (cm −2 (K km s −1 )−1 ) (Bertsch+93). ■ Foreground (local) ISMによる吸収量を推定, NH(X-ray)から差し引く(=SNRとの相互作用分) → X-ray shellに沿った構造が明らかになった
← Image: absorption-corrected X-ray flux (3−10 keV) Contours: ISM proton column density NH (H2+H1) Correlation plot between the Flux and N H (H 2 +H I ) (a) whole, (b) East and (c) West region. Correlation coefficient: ~0.54 (whole region) ISMは西側でclumpy,東側ではdiffuseに分布. ISMの多い領域でX-ray enhance (特に西側)弱いながらもN H (H 2 +H I)とfluxは相関
← Image: Photon index Γ Contours: ISM proton column density N H (H 2 +H I ) ↓  Correlation plot between the Γ and N H (H 2 +H I ) (a) whole, (b) East and (c) West region. SNR全体に渡って, photon index Γの小さな領域がいくつか存在している. ISM richな西側はNH(H₂+H₁)とΓが反相関,東側では、両者の顕著な相関は見られない
■ We interpret the photon index variation as difference of cut-off energy ερ. → The cutoff-energy become large (small) when the value of photon index is small (large). The cutoff-energy ερ is expressed as (Zirakashvili & Aharonian 07),
ερ = 0.55×(v s / 3000 km s −1)²η−1 keV.
where ν , is shock velocity, η is the degree of magnetic field fluctuations (gyro-factor). Here, the shock velocity in the dense clump became ν s,clump = ν s,ambient ( n ambient/n clump where the ambient gas density  nambient = 1 cm −3 and clump density nclump = 10 2 −1 ■ In the west region: clumpy and rich ISM (shock waves will be stalled + strong turbulence) ⇒ small shock speed and small η (η~1; Uchiyama+07) In the east region: diffuse and poor ISM (shock waves will be little decelerated) ⇒ large shock speed and large η Therefore, photon index Γ can be small in both regions. However, the flux excess cannot describe only this scenario.
■ In the west region: clumpy and rich ISM (shock waves will be stalled + strong turbulence) ⇒ small shock speed and small η (η~1; Uchiyama+07) In the east region: diffuse and poor ISM (shock waves will be little decelerated) ⇒ large shock speed and large η Therefore, photon index Γ can be small in both regions. However, the flux excess cannot describe only this scenario. → Perhaps the additional particle acceleration mechanism is working in the ISM rich and clumpy region (e.g., Hoshino+12) ■ X-ray spectroscopy for the young TeV γ-ray SNR RXJ1713 − We reveal the NH (X-ray), Γ and flux maps (+comparing with the ISM) ■ Efficient cosmic-ray acceleration – We can describe the photon index variation as difference of the cut-off energy. – The additional particle acceleration mechanism is working in the ISM rich and clumpy region. − The interacting ISM with SNR is crucial play a role to understanding the efficient CR acceleration. (NANTEN/NANTEN2 CO and Suzaku X-ray datasets make a very strong combination!) ■ CTA will provide more detail information (high angular resolution images, photon index distribution, etc…) and reveal the relationship between the efficient CR acceleration and the ISM distribution. ■ RXJ1713のX-ray filamentary structureとISM – MHD計算の磁場増幅scaleは, ~0.05 pc (Inoue+12). – RXJ1713で確認されているX線の short time variability (~0.05 pc: Uchiyama+07) ⇒ ALMAで~0.05 pcへ迫るCO image with Mopra (Sano in prep.)
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他のガンマ線SNRとISMの相互作用
– RXJ1713の結果の普遍性を探る(HESS J1731, RCW86 etc..) – Thermal X-raysや Hard X-raysとISMの関係は？ (ASTRO-H SXS, HXIに期待) Contours: CO 1-0 (Fukuda+13 submitted to ApJ) RCW86 X-ray image +NANTEN2 CO contours ■
Interacting ISMとしてのHıの重要性
– RXJ1713 SE-rimのcold Hıや, Vela Jr.のHıシェルも重要なISM構成要素→ SNRと相互作用するISMの大半を占めたり, 100個/ccを超えるものも存在RXJ1713 East (Sano+13b in prep.) Vela Jr. (Sano+13c in prep.)多くのSNRについて付随するHIを特定、物理量を明らかにしていくことが肝要