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
CC SNRs are more asymmetric than Ia SNRs (Lopez+09;11)
CC
0104-72.3
Ellipticity
E0102-72
Type Ia
Chandra images of Galactic/Magellanic SNRs
Doesn’t work for SMC SNRs… (Lopez+12)
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
YOU LOSE
Simple Quiz
m9(^Д^)
Suzaku spectrum of
Tycho (Hayato+10)
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 (Type Ia SNR)
W49B (CC SNR)
Artificial
features
(a sort of bgd)
S
i
S Ar
Ca
Fe
Ni
Mg
HY+2008,
Uchida+, in prep.
Ne
Ozawa+2009
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
SN1006 (Type Ia SNR)
W49B (CC SNR)
Artificial
features
(a sort of bgd)
S
i
S Ar
Ca
Fe
Ni
Mg
HY+2008,
Uchida+, in prep.
Ne
Ozawa+2009
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)
Fe-K diagnostics
Extreme cases have been shown
SN1006: Type Ia SNR, Fe lowly-ionized due to a low ambient density and
ejecta stratification with Fe more concentrated toward the center
W49B: CC SNR, Fe over-ionized (recombining),
possibly due to interaction with high-density CSM
… and inhomogeneous ejecta structure?
Red: Si
Blue: Fe
Green: continuum
Other SNRs?
Fe-K diagnostics
- Type Ia and CC SNRs are clearly
separated (CC more 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)
Summary
- X-ray observation of SNRs is one of the best methods to study
stellar/explosive nucleosynthesis. (optically-thin, K-shell emission)
- Understanding of non-equilibrium in ionization is, however,
essential for accurate measurement of element abundances.
- Fe emission in Type Ia SNRs is commonly weak due to low-density
ambient and stratified chemical composition.
- In CC SNRs, on the other hand, Fe is highly ionized, sometime
overionized, possibly due to initial CSM interaction.
- No evidence of a large cavity expected from an “accretion wind”
around Type Ia SNRs, except for RCW86, constraining progenitor
system??