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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

Hiroya Yamaguchi

Harvard-Smithsonian Center for Astrophysics

(+ MIT/RIKEN)

type ia supernovae
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
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)

problems in the sd scenario
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.

problems in the sd scenario1
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?

problems in the sd scenario2
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?

classification of sn progenitors
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)

morphology of snrs
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)

x ray spectra of snrs
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

x ray spectra of snrs1
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

non equilibrium in ionization nei
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)

non equilibrium in ionization nei1
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)

non equilibrium in ionization nei2
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

sn1006 searching for fe emission
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+

sn1006 multiple n e t components in si
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

sn1006 fullband spectrum abundances
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

ejecta stratification in type ia sn snrs
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)

0509 67 5 x ray observations

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)

0509 67 5 x ray observations1

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◉

fe k diagnostics
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?

fe k diagnostics1
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

fe k diagnostics2
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

evidence of cavity csm in ia snrs
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)

dd scenario
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.

dd scenario1
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

low abundance e lement in tycho

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

neutron rich element in ia snrs
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!!

neutron excess in ia progenitors
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

mn cr ratio as an initial m etallicity tracer

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!!

tycho kepler deep obseravations
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?

summary
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)?
w49b peculiar ionization state
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”

w49b possible progenitor
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)