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 = 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

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 mergerDouble Degenerate (DD)重力波放出により接近・合体

(e.g.,Webbink+84)

Problems in the SD scenario1. 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.

Problems in the SD scenario2. No presence of CSM

Nomoto+82

“Accretion wind”Kato & Hachisu 94; Hachisu+01近傍に CSM の存在が期待される

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？

Problems in the SD scenario3. No signal of hydrogen stripped from a companion

SN2005am, SN2005 cf(Leonard+07)

SN2011fe (Shappee+12)

4. Lack of Super Soft SourcesDi Stefano 10, Gilfanov&Bogdan 10, but see Hachisu+10; Wheeler+12

5. Delay Time Distribution (DTD)e.g., Totani+08; Maoz+10

Can we constrain progenitor’s nature from X-ray observations?

Recent works seem to be more supportive of the DD scenario, but we should still have an open mind.

Classification of SN ProgenitorsOptical obs of SNeClassification is relatively straightforward- Spectrum (historically well established) - Luminosity (56Ni yield)

X-ray obs of SNRsClassification (Ia/CC) is (was) controversial in many SNRs- Similar X-ray luminosity- Morphology? SNRs can be spatially resolved, strong advantage of X-ray- Spectrum?

SNe Ia: nuclear reaction energy ~ 1051 ergSNe CC: gravitational energy ~ 1053 erg

99% neutrino + 1% kinetic (~ 1051 erg)

Ia (SD)

Ia (DD) CC (1987A)

=> transformed to thermal energy (X-ray luminosity)

Type Ia

CC

Ellip

ticit

y

Mirror asymmetricity

Morphology of SNRsIa SNRs are more symmetric than CC SNRs (Lopez+09;11)

G344.7-0.1 found to be Type Ia (HY+12)

Chandra images of Galactic/Magellanic SNRs

Reflects nature of explosion and/or environment

SNR E0102-72 (CC) 0104-72.3 (Ia candidate)

Doesn’t work for SMC SNRs…

X-Ray Spectra of SNRsAdvantage- 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

Si

SArCa Fe

Ni

MgNe

Artificial features(a sort of bgd)

Simple Quiz

CC (W49B)Ia (SN1006)

Suzaku spectrum of Tycho (Hayato+10)

X-Ray Spectra of SNRs

Si

SArCa Fe

Ni

MgNe

Artificial features(a sort of bgd)

W49B (CC)

Large foreground extinction makes O/Ne/Mg emission in W49B weak

Absorption for different column density (NH [cm-

2]) SN1006

W49B

Note: although we use NH to describe the column, what we measure in X-rays is the column of metalsYet, weakness of Fe emission in

SN 1006 (Ia SNR) is puzzling => Understanding of NEI

is essential

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

Fe ion population in NEI plasma for kTe = 5 keV

net (cm-3 s)

Ion

fract

ion Fe24+

Fe25+

Fe26+

Fe16+lowly ionized

highly ionized

Fe24+

Fe25+

Fe26+Fe16+

Electron temperature kTe (keV)

CIE

net : “ionization age” ne : electron density t : elapsed time since gas was heated

Non Equilibrium in Ionization (NEI)Fe ion population in NEI plasma for kTe = 5 keV

net (cm-3 s)

Ion

fract

ion Fe24+

Fe25+

Fe26+

Fe16+lowly ionized

highly ionized

net : “ionization age” ne : electron density t : elapsed time since gas was heated

Timescale to reach CIE for ISM t ~ 3 x 104 (ne/1 cm-3)-1 yr

As for ejecta…Time when the masses of swept-up ISM and ejecta becomes comparable

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.

Non Equilibrium in Ionization (NEI)

Full X-ray band

Magnified spectra in the 6-7 keV band (Fe K emission)

Fe-L blend

Fe-K

Observed spectrum (Convolved by Suzaku response)

net = 5x109 1x1010 5x1010 1x1011 3x1011

Ar-like Ne-like C-like Be-likeHe-like

Model spectra of Fe emission [kTe = 5 keV]How does ionization age affect a spectrum? How can we measure ionization age?

H-like

6.42 keV 6.44 keV 6.60 keV 6.64 keV 6.67 keV

6.0 7.0

0.5 10

SN1006: Searching for Fe emission

Fe?

BeppoSAX MECSspectrum

Chandra image

- Prototypical Type Ia SNR, but emission from Fe has never been detected.

- Only one possible detection reported by BeppoSAX- XMM-Newton failed to detect

Vink+00

Suzaku spectrum(HY+08)

Detected! but weak despite of its Type Ia originFe-K centroid ~ 6420eV (< Ne-like) … Corresponding net is ~ 1 x 109 cm-3 s

Fe24+

Fe25+

Fe26+

Fe16+

SN1006: Multiple net Components in Si

Approx with 2-net componentsfor Si and S ejecta

net1 ～ 1×1010 cm-3 snet2 ～ 1×109 cm-3 s

cf. Fe: net ～ 1×109 cm-3 sSi ion fraction @1keV

Si12+

Si13+

Si6+ Si8+

C~O-like He-like

Mg Si

broad feature

S

Reverse shock heats from outer regionOuter ejecta = highly ionizedInner ejecta = lowly ionized

SN1006: Fullband Spectrum & Abundances

ISM (w/ solar abundance)Outer ejecta (net ~ 1010 cm-3 s)Inner ejecta (net ~ 109)Non-thermal (synchrotron)

Fe

Derived abundance ratios compared to the W7 model of Nomoto+84

Outer ejecta

Inner ejecta

Suggests stratified composition with Fe toward the SNR center, which results in the lowly-ionized (thus weak) Fe emission

HY+08

Ejecta Stratification in Type Ia SN/SNRsXMM image of Tycho

Radius (arcmin)

Radial profile

FeSi

Color: Si-KContour: Fe-K

Decourchelle+01

Mazzali+07IME

56NiEnclo

sed

mas

s

SN 2003du(Tanaka+10)

See also Badenes+06

0509-67.5: X-Ray Observations

4 pc15.2arcsec

12.8arcsec

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)?

Blue: Old Ejecta Light-blue: Young EjectaOrange: power-law Green: ISM

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-3 s ⇒ Fe の電離度はやはり低い！

solid : W7 (Nomoto et al. 1984)dashed : WDD3 (Iwamoto et al. 1999)

0509-67.5: X-Ray Observations

4 pc15.2arcsec

12.8arcsec

1D numerical modeling(Badenes+08)

0509-67.5 was a bright SN Ia with a Fe yield of ~ 1M◉

Fe-K diagnosticsType Ia SNRs (e.g., SN1006 & 0509-67.5):

Fe lowly-ionized due to a low ambient densityEjecta 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

Hwang+06

Red: SiBlue: FeGreen: continuum

Other SNRs?

CrMnHe-like Fe Ka

Ni + Fe KbFe-K RRC

H-like FeOzawa+09

Fe-K diagnosticsType Ia

CC

- Type Ia and CC SNRs are clearly separated (Ia always less ionized)- Luminosity of both groups are distributed in the similar range.

(HY+, in prep.)

net = 5x109 1x1010 5x1010 1x1011 3x1011

Can be explained by ionization (and temperture, density effects) --- Measuring ionization state is essential for measuring element abundances!!

Fe-K diagnostics

Type Ia

CC

(HY+, in prep.)

Ionization ages expected if the SNRs have evolved in uniform ISM with typical density

Hachisu+01

Badenes+07

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 Ia SNRs

Evidence of cavity/CSM in Ia SNRs

RCW86 (Williams+11)Unique Ia SNR where the presence of a surrounding cavity is suggested.

Kepler (Reynolds+07)

N103B (Lewis+03)

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

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).

NGC 1718age ~2Gyr, [Fe/H]=-0.7[Mg/Fe]=-0.9±0.3 (Colucci et al. 2012)

TT & B

ekki 2012

Likely, its birth place is the ejecta of SNe Ia.

SN Ia-like abundances of Fe-peak elements

WDD1, WDD2 model from Iwamoto et al. 1999

DD scenario の元素合成モデル

type Fe Cr Mn Ni commentSlow SN Ia 0.41 6.9x10-3 1.1x10-3 7.8x10-3 nucleosynthesis caclulation (this study)

2.5x10-3 1.5x10-3 8.9x10-3 prediction from chemical evolutionprompt SN Ia 0.71 1.7x10-2 7.1x10-3 5.9x10-2 WDD2 model in Iwamoto et al. 1999

in the scheme of SNe Ia 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

already predicted as a result of the merger of two WDs (Pakmor et al. 2010, 2011)TT & Shigeyama 2012

subluminous SNe Ia

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

Low-Abundance Element in TychoSuzaku (Tamagawa+09) Good energy resolution and high sensitivity The first discovery of Cr and Mn lines from Type Ia SNRs

Tamagawa+09

Detection!

Solar abun. Tycho

Fe Si O Fe

Mn Cr Mn Cr

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

Neutron-Rich Element in Ia SNRs

To synthesize such elements, progenitor should be rich with neutronBut, Type Ia progenitor consists mainly of 12C (Z=6) and 16O (Z=8)

Cr: 52Fe (Z=26) → 52Mn (Z=25) → 52Cr (Z=24)Mn: 55Co (Z=27) → 55Fe (Z=26) → 55Mn (Z=25)

O Ne Mg Si S Ar Ca Cr Mn FeFe Co Ni

Proton 8 10 12 14 16 18 20 26 27 28Neutron 8 10 12 14 16 18 20 26 28 28

Heavy elements which have been detected from Type Ia SNR so far

Unequal numbers of protons and neutrons (neutron excess) !

↑Parent nuclides synthesized in the explosion

How did the neutron excess in the progenitor originate?⇒ Found in processes during the progenitor’s evolution!!

Neutron Excess in Ia Progenitors- During the progenitor’s main seq., C, N, and O which act as catalysts for CNO cycle pile up into 14N

Slowest reaction

H-burning: 4He is eventuallysynthesized from 4 protons

increase!

pp-chain

- 14N is converted to 22Ne in He-burning phase through the reactions 14N(a, g)18F(b+, n)18O(a, g)22Ne

C O NeProton 6 8 10Neutron 6 8 12

Elements in Type Ia progenitor (WD)

Increases the neutron excess

- CNO cycle takes place efficiently when C, N, and O are abundant

⇒ Neutron excess (abundance of 22Ne) becomes larger when the progenitor’s metallicity (initial CNO abundances) is high

CNO cycle

Mn/Cr Ratio as an Initial Metallicity TracerDuring 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 ArCa Cr Mn Fe, Ni

Mn and Ni are sensitiveto neutron excess!!

Mn/Cr ratio is an good tracer of the initial progenitor’s metallicity!

Badenes+08 noted a correlation b/wMn/Cr mass ratio and metallicity Z MMn/MCr = 5.3 x Z0.65

For the progenitor of Tycho’s SN,(MMn/MCr = 0.74±0.47) yields a supersolar metallicity - Z = 0.048 (0.012 － 0.099) - Large uncertainty, but definitely not subsolar (Z<0.01)

Tycho & Kepler Deep Obseravations

Mn/Cr Ni/Fe (Cr+Mn)/Fe

Tam

agaw

a+08

Old

100k

sNe

w 40

0ks

Sum

500

ks

Tycho KeplerOld

New

Sum

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?

Summary- SNe Ia 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 Ia SNRs 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 Ia SNRs, except for RCW86, constraining progenitor system??- Low abundance element in Tycho and Kepler can constrain their progenitors’ nature (not only metallicity but SD/DD)?

W49B: Peculiar Ionization State

- 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

“Recombining NEI” in SNRs is not unique => Need to define “recombination age”

Cr MnHe-like Fe Ka

Ni + Fe Kb

Fe-K RRC

H-like Fe

Ozawa+09

Ejecta is highly ionized to be He-likeRadiative recombination continuum

Fe25+ + e- → Fe24+ + hn … indicates presence of a large fraction

of H-like FeMeasured kTe ~ 1.5 keV

Temperature (keV)

Fe24+

Fe25+

Fe26+Fe16+

Fe ion population in a CIE plasma

W49B: Possible Progenitor

blast wave

2nd reverse shock

reverse shockBlast wave breakout into ISM

BW speed becomes faster and expand adiabatically, resulting in rapid cooling with “frozen” ionization state

Shimizu+12Explosion in dense CSM - Numerical (Shimizu+12)- Analytical, more progenitor- oriented (Moriya 12)

RSG case (vw ~ 10 km/s) WR case (vw ~ 1000 km/s)

Type II-P or IIn could be a progenitor of a recombining SNR (Moriya 12)