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 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
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 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 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
Optical obs of SNe
Classification is relatively
straightforward
- Spectrum (historically
well established)
- Luminosity (56Ni yield)
X-ray obs of SNRs
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 (SD)
Ia (DD)
CC (1987A)
SNe Ia: 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
Ia SNRs are more symmetric than CC SNRs (Lopez+09;11)
Ellipticity
CC
Type Ia
Chandra images of Galactic/Magellanic SNRs
Doesn’t work for SMC SNRs…
Mirror asymmetricity
Reflects nature of explosion
and/or environment
G344.7-0.1 found to be Type Ia (HY+12)
SNR E0102-72 (CC)
0104-72.3 (Ia candidate)
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
Artificial
features
(a sort of bgd)
Ia (SN1006)
Mg
Ne
S
i
S Ar
Ca
CC (W49B)
Fe
Ni
X-Ray Spectra of SNRs
Absorption for
different column
density (NH [cm-2])
SN1006
Large foreground extinction makes
O/Ne/Mg emission in W49B weak
Note: although we use NH to describe
the column, what we measure in
X-rays is the column of metals
Yet, weakness of Fe emission in
SN 1006 (Ia SNR) is puzzling
=> Understanding of NEI
is essential
W49B
Artificial
features
(a sort of bgd)
Mg
Ne
S
i
S Ar
Ca
W49B (CC)
Fe
Ni
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
Fe16+
highly
ionized
Ion fraction
lowly
ionized
Fe24+
+
Fe24+
Fe26+
Fe25+
CIE
Fe25+
Fe26+
net (cm-3 s)
Fe16
Electron temperature kTe (keV)
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
Fe16+
highly
ionized
ne : electron density
t : elapsed time since gas was heated
Fe24+
Ion fraction
lowly
ionized
net : “ionization age”
Fe25+
Fe26+
Timescale to reach CIE for ISM
t ~ 3 x 104 (ne/1 cm-3)-1 yr
net (cm-3 s)
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)
How does ionization age affect a spectrum? How can we measure ionization age?
Model spectra of Fe emission [kTe = 5 keV]
1x1010
5x1010
1x1011
net = 5x109
3x1011
Fe-K
Fe-L blend
Full X-ray band
0.5
10
Magnified spectra in the 6-7 keV band (Fe K emission)
C-like
Ne-like
Ar-like
6.0
Be-like
He-like
H-like
7.0
Observed spectrum (Convolved by Suzaku response)
6.42 keV
6.44 keV
6.60 keV
6.64 keV
6.67 keV
SN1006: Searching for Fe emission
- Prototypical Type Ia SNR, but emission from Fe has never been detected.
BeppoSAX MECS
spectrum
Fe?
Chandra image
- Only one possible detection
reported by BeppoSAX
- XMM-Newton failed to detect
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+
Suzaku spectrum
(HY+08)
Fe24+
Fe25+
Fe26+
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
Si6+ Si8+
Si12+
Si13+
Approx with 2-net components
for Si and S ejecta
net1 ～ 1×1010 cm-3 s
net2 ～ 1×109 cm-3 s
Si ion fraction @1keV
cf. Fe: net ～ 1×109 cm-3 s
SN1006: Fullband Spectrum & Abundances
Derived abundance ratios compared
to the W7 model of Nomoto+84
Fe
Outer ejecta
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
XMM image of Tycho
SN 2003du
(Tanaka+10)
Color: Si-K
Contour: Fe-K
Radial
profile
Si
Fe
Radius (arcmin)
Enclosed mass
Decourchelle+01
IME
Mazzali+07
56Ni
See also
Badenes+06
0509-67.5: X-Ray Observations
The youngest SNR in the LMC (~400 yr: Rest+08)
12.8arcsec
Chandra revealed clear shell structure of the ejecta
& the western “Fe knot” (Warren+04)
– due to off-center ignition (e.g., Maeda+10)?
15.2arcsec
4 pc
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)
Blue: Old Ejecta
Light-blue: Young Ejecta
Orange: power-law
Green: ISM
0509-67.5: X-Ray Observations
12.8arcsec
15.2arcsec
4 pc
1D numerical modeling
(Badenes+08)
0509-67.5 was a bright SN Ia with a Fe yield of ~ 1M◉
Fe-K diagnostics
Type Ia SNRs (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
Cr Mn
He-like Fe Ka
Ni + Fe Kb
Fe-K RRC
H-like Fe
Ozawa+09
Hwang+06
Red: Si
Blue: Fe
Green:
continuum
Other SNRs?
Fe-K diagnostics
- Type Ia and CC SNRs are clearly
separated (Ia always less ionized)
Type Ia
- Luminosity of both groups are
distributed in the similar range.
CC
Can be explained by ionization
(and temperture, density effects)
--- Measuring ionization state is
essential for measuring
element abundances!!
(HY+, in prep.)
net = 5x109
1x1010
5x1010
1x1011
3x1011
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 Ia SNRs
Badenes+07
Evidence of cavity/CSM in Ia SNRs
Kepler (Reynolds+07)
RCW86 (Williams+11)
Unique Ia SNR where the presence of
a surrounding cavity is suggested.
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
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 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 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
subluminous SNe Ia
already predicted as a result of the merger of
two WDs (Pakmor et al. 2010, 2011)
TT & Shigeyama 2012
Mn
Ni
comment
type
Fe
Cr
Slow 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 evolution
prompt SN Ia
0.71
1.7x10-2 7.1x10-3 5.9x10-2 WDD2 model in Iwamoto et al. 1999
Low-Abundance Element in Tycho
Suzaku (Tamagawa+09)
Good energy resolution and high sensitivity
The first discovery of Cr and Mn lines from Type Ia SNRs
Detection!
Tamagawa+09
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
Tycho
Solar abun.
Fe
Si O
Mn Cr
Fe
Mn Cr
Neutron-Rich Element in Ia SNRs
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
Cr
Mn
Fe
Fe
Co
Ni
O
Ne Mg
Si
S
Ar
Ca
Proton
8
10
12
14
16
18
20
26
27
28
Neutron
8
10
12
14
16
18
20
26
28
28
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
- 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
H-burning: 4He is eventually
synthesized from 4 protons
CNO cycle
increase!
Elements in Type Ia progenitor (WD)
C
O
Ne
Proton
6
8
10
Neutron
6
8
12
Increases the
neutron excess
Slowest reaction
- 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
pp-chain
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
Mn/Cr ratio is an good tracer of
the initial progenitor’s metallicity!
12C 16O
22Ne
Mg Si S Ar
Ca Cr Mn Fe, Ni
Mn and Ni are sensitive
to neutron excess!!
Badenes+08 noted a correlation b/w
Mn/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)
(Cr+Mn)/Fe
Sum
New
Old
Tycho
Ni/Fe
Sum 500ks
Mn/Cr
New 400ks
Old 100ks
Tamagawa+08
Tycho & Kepler Deep Obseravations
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
- 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
Cr
Ejecta is highly ionized to be He-like
He-like Fe Ka
Mn
Radiative recombination continuum
Fe25+ + e- → Fe24+ + hn
… indicates presence of a large fraction
of H-like Fe
Ni + Fe Kb
Fe-K RRC
H-like Fe
Measured kTe ~ 1.5 keV
Ozawa+09
Fe ion population in a CIE plasma
Fe16+
Fe26+
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
Explosion in dense CSM
Shimizu+12
- Numerical (Shimizu+12)
- Analytical, more progenitororiented (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 or IIn
could be a progenitor
of a recombining SNR
(Moriya 12)
RSG case (vw ~ 10 km/s)
WR case (vw ~ 1000 km/s)