Paolo A. Mazzali

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Using observables to understand SNe Ia Paolo A. Mazzali

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Recent Progress on SNe IaPaolo A. Mazzali
SNe Ia @ maximum
SNe Ia: late-time spectra
1998
Δm15(B)
1.93
1.77
1.27
1.51
0.87
Typical SNe Ia Early time: Lum-LC width Late time: Lum-Em line w.
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Phillips 1993 PM et al. 1998
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Abundance Stratification Models of spectral sequence give composition layering
SN 2002bo: bright [m15(B)=1.15] SN 2004eo: dim [m15(B)=1.45] (Stehle et al. 2005) (Mazzali et al. 2008)
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Late-time spectra Full view of inner ejecta (56Ni zone)
Monte Carlo LC code + NLTE nebular code (no radiative transfer)
• Estimate masses
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Abundance distribution in two SNe
SN2002bo (brighter) has more burning
SN 2002bo
SN 2004eo
SN 2011fe • Use density and abundance
distribution to compute synthetic
bolometric LC with Montecarlo
Zorro: composition layering, 56Ni and IME compensate
Abundances
• Stable Fe group isotopes contribute to opacity
• Very good correlation between Σ(NSE) and Δm15(B)
Not all SNe Ia fall on Phillips relation,
not all SNe Ia are “normal”
2003hv
2002cx
2009dc
• cool TiII lines, rapid LC evolution: Δm(B)15=1.8 mag
• Solution: M(Ch) ejecta with low Ek (1051erg), 56Ni (0.1 M)
• Still an extension of normal SNe Ia, but inefficient (Ashall et al 2016)
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The bright end: the peculiar SN1991T: still M(Ch)
• M(Ch) model with outer distribution of 56Ni can explain evolution of spectra
and LC. Efficient burning, high M(56Ni)≅0.78M leads to high T, FeIII lines.
• Difficult to distinguish W7 from energetic Delayed Detonation.
• Other 91T-like SNe may be variations on theme (Sasdelli et al. 2014) 5 Aug 2019 SN Ia meeting, Lijiang 24
5 Aug 2019 SN Ia meeting, Lijiang
Normal SNe Ia are compatible with
Chandrasekhar-mass explosions
• Problems include:
– Lack of progenitors
• Most WDs come from low-mass stars, and have masses of 0.4-0.8 M
– Where is the accreting H ?
• Searches in both early and late-time spectra so far have failed
– Where is the companion?
• No signatures in light curves, typically no evidence of interaction
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double-degenerate scenario (WD merger) • Better predicted rates, range of masses (both sub- and super-Chandra)
• A problem is the lack of symmetry
Other proposed scenarios
• He accretion
– He shell is prone to detonation, which can lead to the
explosion of sub-M(Ch) WDs (“edge-lit”) (Livne / Arnett etc.)
• WD collisions
– Direct collision can be more common in dense
environments such as globular clusters (Rosswog) or in
triple systems (Katz/Kuschnir)
• Core-degenerate
– WD inside envelope of RG accretes material from it (Soker)
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Can we find evidence of different channels?
1991bg-like
SNe 1986G, 1991T: still M(Ch)? SN 2002cx-like: pure deflagrations?
SN 2009dc “super-Chandra” ? SNe 2007on, 2011iv: collisions?
2005hk
SN 2002cx, 2005hk
• Late: spectra DO NOT become nebular
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SN 2002cx, 2005hk
• A pure deflagration gives good fits
• M(56Ni) ~ 0.2 M
SN 2003hv: m15(B)=1.6 mag
• One of very few well-observed SNe in the “gap”
• Early-time spectra appear normal, but
• 56Ni from LC peak (0.4 M) ≠ LC tail (0.2 M)
(Leloudas et al. 2009)
SN 2003hv: reduced inner density
• Large FeIII/FeII ratio: high ionization: low density
• Model with M ≅ 1.2 M and reduced inner density
reproduces nebular spectrum (Mazzali et al. 2011)
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SN2003hv: a sub-Chandra event?
• Reduced density leads to an earlier LC peak (~12 days)
• M(56Ni) = 0.2 M, M~1.1 M
• Estimate of M(56Ni) from LC peak inaccurate if trise not known
• Density structure similar to that of sub-Chandra explosions
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What’s special with SN1991bg?
• It made too little 56Ni, even for a deflagration
• Nebular spectra evolve significantly, inconsistent with any M(Ch) density profile
• Inner nebula dominated by [FeIII] emission: high ionization
• This implies low densities, again
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Was SN1991bg sub-Chandra?
• Early-time spectra require low Ek, i.e. little M at high vel.
• Abundances show unburned material, IME down to low vel.
• Different models are possible, as long as E/M is small
SN2005bl
How to solve SN 1991bg
• A modified density, esp. in the innermost zones,
makes it possible to reproduce the spectral evolution
• The ionization is higher mostly at very low velocities (PM & S. Hachinger, 2012)
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Are SN1991bg-like SNe mergers?
• Although M ~ 1.1 M, key to nebular behaviour is actually low density in innermost region, a feature of merger models.
• Very early data could be useful
Do collisions exist? SNe 2007on and 2011iv
• SN 2007on famous for its double-
peaked NaID emission line
– SN 2007on, ΔmB(15)=1.96 mag
– SN 2011iv, ΔmB(15)=1.73 mag
• They both fall off the Phillips relation:
too luminous for their LC shape
• Both located on outskirts of the same
passive host, suggestive of old
progenitors
features 5 Aug 2019 SN Ia meeting, Lijiang 37
Modelling 07on: not just geometry
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Spectrum appears to be the sum of
two separate, “narrow-line” spectra.
shifted, resp., but just adding two
equal components does not work.
The two components are different:
Their ionization degree is not the
same, indicating that one spectrum
is hotter (i.e. it comes from a more
highly ionised, less dense nebula),
the other cooler (and less ionised).
Modelling 07on: 2-components
Comp. 1) Low ionization:
M (inside v) = 0.11M
Comp. 2) High ionization:
M (inside v) = 0.09 M
Relative shift: 5750 km/s
Consistent with two separate
SN2009dc and “super-Chandra” SNe Ia
• Very bright, late (~23d) peak [M(56Ni) >~ M(Ch)?]
• Hot early spectra
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Our favourite solution: SN Ia + CSM
• A low-energy SN Ia interacting
with H- and He-free CSM gives
a consistent solution, including
Results • Most SNe Ia (including normal ones):
– Total mass burned is constant [~M(Ch)]
– Ejecta show stratified composition very similar to that of Delayed Detonation models
– Reason for range of 56Ni mass yet unknown
– Total NSE mass determines LC shape
• Exceptions (mostly low-Lum, peculiar SNe Ia):
– Different masses (sub-Ch), explosion modes revealed by peculiar location in Lum-LC shape rel’n, may be mergers, collisions, He accretors
– Super-Chandras may be SNe Ia interacting with H/He-free CSM
What is the relative incidence of different subtypes?
Luminosity distribution of SNe Ia
• There seem to be two separate components. Are these
representative of two populations/channels? (Ashall 2016)
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SNe Ia in Spiral galaxies are more
uniform than those in passive galaxies WLR corrected for extinction MB and ΔM15(B) Distributions
Ashall et al 2016
Spirals contain a fraction with a passive
galaxy Luminosity distribution
Correcting for the
Spirals better
standard candles
Conclusions
– Some (e.g. 91T, 86G) are just extreme normals with
high/low M(56Ni), Ek
• SNe Ia with M ≠ M(Ch) tend not to obey WLR
• Super-Chandras and 91bg’s may be mergers
• Passive galaxies like low-Lum, peculiar (old?) SNe Ia
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