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Ia 型超新星 の 元素合成と その周辺環境

Ia 型超新星 の 元素合成と その周辺環境. Hiroya Yamaguchi Harvard-Smithsonian Center for Astrophysics (+ MIT/RIKEN). Type Ia Supernovae. 現象論的には、おおよその特徴はわかっている. - 可視光スペクトルに水素の吸収線がない - Si/S/Fe などを豊富に含む - E = 10 51 erg, M B,max ~ -19 mag - エネルギー源は 56 Ni(& 56 Co) の崩壊ガンマ線 - 楕円銀河でも起こる → 小質量星起源を示唆

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Ia 型超新星 の 元素合成と その周辺環境

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  1. Ia型超新星の元素合成とその周辺環境 Hiroya Yamaguchi Harvard-Smithsonian Center for Astrophysics (+ MIT/RIKEN)

  2. Type Ia Supernovae 現象論的には、おおよその特徴はわかっている • - 可視光スペクトルに水素の吸収線がない • - Si/S/Fe などを豊富に含む • - E = 1051 erg, M B,max~ -19 mag • - エネルギー源は56Ni(&56Co)の崩壊ガンマ線 • - 楕円銀河でも起こる → 小質量星起源を示唆 • ejectaの質量は ~1.4M◉ • but see e.g, Shigeyama+92, Yamanaka+09 • → 白色矮星の核暴走（Chandrasekher mass） - Phillips relation: 明るいSN Iaほどゆっくり減光 (Pillips+93) → 「(補正可能な)標準光源」 → 宇宙の加速膨張を発見 (e.g., Perlmutter+99; 2011年ノーベル賞) - 宇宙に存在する鉄族元素の主要起源

  3. Type Ia Progenitor Issue 実は、爆発機構どころか親星もわかっていない - 少なくとも１つの白色矮星が寄与するのは間違いない WDの典型的な質量は 0.6-0.8M◉ - 爆発的核融合が始まるためには、Chandrasekhar massに近づく必要 … どうやって？ WD + MS/sub-G Single Degenerate (SD) 伴星からの質量降着によりWDが太る (e.g., Whelan+73) WD + WD merger Double Degenerate (DD) 重力波放出により接近・合体 (e.g.,Webbink+84)

  4. Problems in the SD scenario 1. No “survivor” 爆発後に伴星が残る(e.g., Pan+12)はずだが、 その観測事例がない(e.g., Schaefer+12) but see Di Stefano+12: a survivor should be too dim to detect LMC SNR 0509-67.5 (Schaefer+12) SN2011fe (Li+11; Shappee+12), SN1006 (González Hernández+12) Tycho: “Tycho G” was suggested to be the companion by (Ruiz-Lapuente+04) but questioned by Ihara+07; Gonzalez Hernandez+09; etc.

  5. Problems in the SD scenario 2. No presence of CSM “Accretion wind” Kato & Hachisu 94; Hachisu+01 近傍にCSMの存在が期待される Nomoto+82 e.g., SN2011fe (Margutti+12) Hughes+07, Horesh+11, Chomiuk+11, Hancock+11 but see Taddia+12; Patnaude+12 但し、上記シナリオでも最後まで 降着風が続く必要は必ずしもない？

  6. Problems in the SD scenario 3. No signal of hydrogen stripped from a companion SN2005am, SN2005 cf (Leonard+07) SN2011fe (Shappee+12) 4. Lack of Super Soft Sources Di Stefano 10, Gilfanov&Bogdan 10, but see Hachisu+10; Wheeler+12 5. Delay Time Distribution (DTD) e.g., Totani+08; Maoz+10 Recent works seem to be more supportive of the DD scenario, but we should still have an open mind. Can we constrain progenitor’s nature from X-ray observations?

  7. Classification of SN Progenitors Optical obs of SNe Classification is relatively straightforward - Spectrum (historically well established) - Luminosity (56Ni yield) X-ray obs of SNRs Ia (SD) Classification (Ia/CC) is (was) controversial in many SNRs - Similar X-ray luminosity - Morphology? SNRs can be spatially resolved, strong advantage of X-ray - Spectrum? Ia (DD) CC (1987A) SNeIa: nuclear reaction energy ~ 1051 erg SNe CC: gravitational energy ~ 1053 erg 99% neutrino + 1% kinetic (~ 1051 erg) => transformed to thermal energy (X-ray luminosity)

  8. Morphology of SNRs IaSNRs are more symmetric than CC SNRs (Lopez+09;11) CC Type Ia Ellipticity Chandra images of Galactic/MagellanicSNRs Doesn’t work for SMC SNRs… Mirror asymmetricity Reflects nature of explosion and/or environment SNR E0102-72 (CC) 0104-72.3 (Ia candidate) G344.7-0.1 found to be Type Ia (HY+12)

  9. X-Ray Spectra of SNRs Advantage - Optically thin (self absorption is almost negligible, but see Miyata+08) - K-shell emission from He- & H-like atoms (kTe ~ hn ~ 0.1–10 keV, comparable to K-shell potential), so physics is simple Suzaku spectrum of Tycho (Hayato+10) Simple Quiz S Si Fe Ar Ca Artificial features (a sort of bgd) Ni CC (W49B) Ia (SN1006) Mg Ne

  10. X-Ray Spectra of SNRs Large foreground extinction makes O/Ne/Mg emission in W49B weak Absorption for different column density (NH [cm-2]) Note: although we use NH to describe the column, what we measure in X-rays is the column of metals SN1006 Yet, weakness of Fe emission in SN 1006 (Ia SNR) is puzzling => Understanding of NEI is essential W49B S Si Fe Ar Ca Artificial features (a sort of bgd) Ni W49B (CC) Mg Ne

  11. Non Equilibrium in Ionization (NEI) Pre-shocked metals in ISM/ejecta are almost neutral (unionized) Shock-heated electrons gradually ionize atoms by collision, but ionization proceeds very slowly compared to heating Fe24+ Fe26+ Fe16+ Fe25+ Fe ion population in NEIplasma for kTe = 5 keV highly ionized lowly ionized Fe16+ CIE Fe24+ Fe25+ Ion fraction Electron temperature kTe (keV) net: “ionization age” ne: electron density t: elapsed time since gas was heated Fe26+ net (cm-3s)

  12. Non Equilibrium in Ionization (NEI) net: “ionization age” ne: electron density t: elapsed time since gas was heated highly ionized lowly ionized Timescale to reach CIE for ISM t ~ 3 x 104 (ne/1 cm-3)-1 yr As for ejecta… Fe ion population in NEIplasma for kTe = 5 keV Time when the masses of swept-up ISM and ejecta becomes comparable Fe16+ Fe24+ Fe25+ Ion fraction Ionization state for the ejecta becomes almost “frozen” after an SNR evolved. Ionization age for the ejecta strongly depends on the initial CSM density rather than its age. Fe26+ net (cm-3s)

  13. Non Equilibrium in Ionization (NEI) How does ionization age affect a spectrum? How can we measure ionization age? Model spectra of Fe emission [kTe = 5 keV] net = 5x1091x1010 5x1010 1x10113x1011 Fe-K Fe-L blend Full X-ray band 0.5 10 Magnified spectra in the 6-7 keV band (Fe K emission) He-like Be-like C-like Ne-like Ar-like H-like 6.0 7.0 Observed spectrum (Convolved by Suzaku response) 6.60 keV 6.67 keV 6.44 keV 6.42 keV 6.64 keV

  14. SN1006: Searching for Fe emission • Prototypical Type Ia SNR, but emission from Fe has never been detected. - Only one possible detection reported by BeppoSAX - XMM-Newton failed to detect BeppoSAX MECS spectrum Fe? Chandra image Vink+00 Detected! but weak despite of its Type Ia origin Fe-K centroid ~ 6420eV (< Ne-like) … Corresponding net is ~ 1 x 109 cm-3 s Fe16+ Fe24+ Suzaku spectrum (HY+08) Fe25+ Fe26+

  15. SN1006: Multiple net Components in Si broad feature Mg Si S C~O-like He-like Reverse shock heats from outer region Outer ejecta = highly ionized Inner ejecta = lowly ionized Si8+ Si6+ Approx with 2-net components for Si and S ejecta net1～ 1×1010 cm-3 s net2～ 1×109 cm-3 s cf. Fe: net ～ 1×109 cm-3 s Si12+ Si13+ Si ion fraction @1keV

  16. SN1006: Fullband Spectrum & Abundances Derived abundance ratios compared to the W7 model of Nomoto+84 Outer ejecta Fe HY+08 Inner ejecta ISM (w/ solar abundance) Outer ejecta(net ~ 1010 cm-3 s) Inner ejecta(net ~ 109) Non-thermal (synchrotron) Suggests stratified composition with Fe toward the SNR center, which results in the lowly-ionized (thus weak) Fe emission

  17. Ejecta Stratification in Type Ia SN/SNRs XMM image of Tycho Enclosed mass IME SN 2003du (Tanaka+10) Decourchelle+01 56Ni Color: Si-K Contour: Fe-K Radial profile Mazzali+07 Si Fe See also Badenes+06 Radius (arcmin)

  18. Suzaku observation (HY 08, Dthesis) - Fe + 一部のSi : net = 3.5×109 cm-3 s - その他の元素 : net = 1.4×1010 cm-3s ⇒ Feの電離度はやはり低い！ 12.8arcsec Blue: Old Ejecta Light-blue: Young Ejecta Orange: power-law Green: ISM 15.2arcsec 0509-67.5: X-Ray Observations The youngest SNR in the LMC (~400 yr: Rest+08) Chandra revealed clear shell structure of the ejecta & the western “Fe knot” (Warren+04) – due to off-center ignition (e.g., Maeda+10)? 4 pc solid : W7 (Nomoto et al. 1984) dashed : WDD3 (Iwamoto et al. 1999)

  19. 12.8arcsec 15.2arcsec 0509-67.5: X-Ray Observations 4 pc 1D numerical modeling (Badenes+08) 0509-67.5 was a bright SN Ia with a Fe yield of ~ 1M◉

  20. Fe-K diagnostics Type IaSNRs (e.g., SN1006 & 0509-67.5): Fe lowly-ionized due to a low ambient density Ejecta stratification with Fe more concentrated toward the center CC SNRs: Ejecta is more mixed, e.g., Cas A (Hwang+06), G292+1.8 (Park+07) Associated with dense CSM/MCs … sometime causes “over-ionization” in plasma e.g., W49B (Ozawa+09), IC443 (HY+09), HY+12 for review see also an analytical work by Moriya+12 to constrain their progenitors He-like Fe Ka Cr Mn Ni + Fe Kb Fe-K RRC H-like Fe Hwang+06 Red: Si Blue: Fe Green: continuum Ozawa+09 Other SNRs?

  21. Fe-K diagnostics - Type Ia and CCSNRs are clearly separated (Ia always less ionized) - Luminosity of both groups are distributed in the similar range. Type Ia CC Can be explained by ionization (and temperture, density effects) --- Measuring ionization state is essential for measuring element abundances!! (HY+, in prep.) net = 5x1091x1010 5x1010 1x10113x1011

  22. Fe-K diagnostics Ionization ages expected if the SNRs have evolved in uniform ISM with typical density Type Ia CC Hachisu+01 (HY+, in prep.) If the SD scenario is the case, a large, low-density cavity is expected around the progenitor No evidence of an “accretion wind” and a resultant cavity but for a few Type IaSNRs Badenes+07

  23. Evidence of cavity/CSM in IaSNRs Kepler (Reynolds+07) RCW86 (Williams+11) Unique Ia SNR where the presence of a surrounding cavity is suggested. N103B (Lewis+03)

  24. DD scenarioの元素合成モデル SNSNR12 超新星と超新星残骸の融合研究会 (10/15-17 @国立天文台) 辻本拓司さんの報告より SN Ia-like abundances of Fe-peak elements NGC 1718 age ~2Gyr, [Fe/H]=-0.7 [Mg/Fe]=-0.9±0.3 (Colucci et al. 2012) WDD1, WDD2 model from Iwamoto et al. 1999 TT & Bekki 2012 Such an extremely low ratio (≤-0.6) is outside any observed Al-Mg anticorrelations (>-0.3) as well as by the prediction from nucleosynthesis calculations on any SNe II (>-0.2). Likely, its birth place is the ejecta of SNe Ia.

  25. DD scenarioの元素合成モデル SNSNR12 超新星と超新星残骸の融合研究会 (10/15-17 @国立天文台) 辻本拓司さんの報告より in the scheme of SNeIa resulting from a 0.8+0.6 M⊙ white dwarf merger the explosion of a WD with the mass 0.8 M⊙ accreting 0.6 M⊙ matter at the mass accretion rate of 0.07 M⊙ s-1 a dim SN Ia after spending more than 1 Gyr from the birth subluminousSNeIa already predicted as a result of the merger of two WDs(Pakmor et al. 2010, 2011) TT & Shigeyama 2012

  26. Detection! Tamagawa+09 Low-Abundance Element in Tycho Suzaku (Tamagawa+09) Good energy resolution and high sensitivity The first discovery of Cr and Mn lines from Type IaSNRs Tycho Solar abun. Cr and Mn very low abundant elements Cr/Fe ~ Mn/Fe ~ 0.01, in solar Cr/Fe = 0.022 Mn/Fe = 0.014 in Tycho’s SNR Fe Si O Fe Mn Cr Mn Cr

  27. Neutron-Rich Element in IaSNRs Cr: 52Fe (Z=26) → 52Mn (Z=25) → 52Cr (Z=24) Mn: 55Co (Z=27) → 55Fe (Z=26) → 55Mn (Z=25) ↑ Parent nuclides synthesized in the explosion Heavy elements which have been detected from Type Ia SNR so far Unequal numbers of protons and neutrons (neutron excess) ! To synthesize such elements, progenitor should be rich with neutron But, Type Ia progenitor consists mainly of 12C (Z=6) and 16O (Z=8) How did the neutron excess in the progenitor originate? ⇒ Found in processes during the progenitor’s evolution!!

  28. Neutron Excess in Ia Progenitors H-burning: 4He is eventually synthesized from 4 protons - During the progenitor’s main seq., C, N, and O which act as catalysts for CNO cycle pile up into 14N - 14N is converted to 22Ne in He-burning phase through the reactions 14N(a, g)18F(b+, n)18O(a, g)22Ne CNO cycle increase! Elements in Type Ia progenitor (WD) Increases the neutron excess Slowest reaction - CNO cycle takes place efficiently when C, N, and O are abundant pp-chain ⇒ Neutron excess (abundance of 22Ne) becomes larger when the progenitor’s metallicity (initial CNO abundances) is high

  29. Badenes+08 noted a correlation b/w Mn/Cr mass ratio and metallicityZ MMn/MCr = 5.3 xZ0.65 For the progenitor of Tycho’s SN, (MMn/MCr = 0.74±0.47) yields a supersolarmetallicity - Z = 0.048 (0.012－0.099) - Large uncertainty, but definitely not subsolar (Z<0.01) Mn/Cr Ratio as an Initial Metallicity Tracer During Type Ia SN explosion: 52Cr and 55Mn are synthesized together (as 52Fe and 55Co) in incomplete Si burning layer (e.g., Iwamoto+99) - The yield of 55Mn (neutron-rich nuclide) would be sensitive to the neutron excess due to 22Ne - 52Cr is NOT sensitive to neutron excess 12C 16O 22Ne Mg Si S Ar Ca Cr MnFe, Ni Mn/Cr ratio is an good tracer of the initial progenitor’s metallicity! Mnand Ni aresensitive to neutron excess!!

  30. Tycho & Kepler Deep Obseravations Mn/Cr Ni/Fe (Cr+Mn)/Fe Tamagawa+08 Old 100ks Sum 500ks New 400ks New Sum Old Tycho Kepler Tycho Kepler Tycho Kepler - Mn/Cr ratio はKepler > Tycho: high metallicity in Kepler? - Keplerは Ni/Fe比が極めて大きい: DD scenario unlikely? Ni/Fe < 0.3 (Kerkwijk+10) - (Cr+Mn)/Fe はKepler < Tycho: assuming SD, Kepler is brighter?

  31. Summary • SNeIa progenitor issue is one of the most intriguing subjects of • the recent astrophysics/astronomy. • X-ray observation of SNRs help study stellar/explosive • nucleosynthesis (optically-thin, K-shell emission), plus progenitors’ • nature (mass loss, metallicity) and environment • - Understanding of non-equilibrium in ionization is, however, • essential for accurate measurement of element abundances. • Fe emission in Type IaSNRs is commonly weak, despite a large • yield of this element. This is due to low-density ambient and • stratified chemical composition. • - No evidence of a large cavity expected from an “accretion wind” • around Type IaSNRs, except for RCW86, constraining progenitor • system?? • - Low abundance element in Tycho and Kepler can constrain their • progenitors’ nature(not only metallicity but SD/DD)?

  32. W49B: Peculiar Ionization State Ejecta is highly ionized to be He-like Radiativerecombination continuum Fe25+ + e- → Fe24+ + hn … indicates presence of a large fraction of H-like Fe He-like Fe Ka Cr Mn Ni + Fe Kb Fe-K RRC H-like Fe Measured kTe ~ 1.5 keV Ozawa+09 Fe ion population in a CIE plasma Fe26+ Fe16+ Fe24+ Fe25+ - RRC can be enhanced only when the plasma is recombining (e.g., photo-ionized plasma) Similar recombining SNRs - IC443 (HY+09) - SNR 0506-68 (Broersen+11) - other 3 & a few candidates Temperature (keV) “Recombining NEI” in SNRs is not unique => Need to define “recombination age”

  33. W49B: Possible Progenitor Explosion in dense CSM Shimizu+12 - Numerical (Shimizu+12) - Analytical, more progenitor- oriented (Moriya 12) blast wave Blast wave breakout into ISM BW speed becomes faster and expand adiabatically, resulting in rapid cooling with “frozen” ionization state reverse shock 2nd reverse shock Type II-P orIIn could be a progenitor of a recombining SNR (Moriya 12) RSG case (vw ~ 10 km/s) WR case (vw ~ 1000 km/s)

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