Type Ia Supernovae
Progenitors
Type Ia Supernovae
Historical defining
characteristics:
Generally, lack of lines of
hydrogen
Contain a strong Si II
absorption feature
(6355Å shifted to ~6100Å)
Observational Characteristics
Homogeneity: nearly 60% homogeneous in terms of spectra, light curves, peak
absolute magnitudes MB ~ -18.8+5log(Ho/74)
Inhomogeneity: differences in spectra, light curves, do exist.
In terms of explosion strength, order:
Very weak, e.g.
SN 1991bg, SN 1992k
Weak, e.g. SN 1986G
Normal, ~60%
Very bright, e.g. SN 1991T, ~20%
The following simple facts
Energy:
½(~104 km/s)2 ~ ECO->Fe
Degeneracy:
Explosive event
Spectrum:
Generally no hydrogen
Delay:
Explosions can occur with long delay after
cessation of star formation.
Basic model:
Thermonuclear disruption of
mass-accreting white dwarf.
Note:
Flame physics is still an unsolved problem,
deflagration to detonation?
Why is identifying the
progenitors so important?
The fact that we still don’t
know the progenitors of
some of the most dramatic
explosions – a major
embarrassment.
For dark energy properties
we need to understand the
evolution of the luminosity
with cosmic time.
Feedback – radiative,
kinetic, nucleosynthetic
input into galaxy evolution.
Composition of accreting WD
He
C-O
• Form at Mwd ≲ 0.45M☉
• Can explode at ∼ 0.7M☉ central
He ignition
• But composition of ejected matter:
He + 56Ni + decay products
Inconsistent with observations
O-Ne-Mg
• Form from M ∼ 8-11.5M☉
• But not numerous enough
and expected to collapse to
NS rather than explode
No
No
Yes
At what mass does the WD
explode?
Chandrasekhar mass
carbon igniters
Carbon ignites at center:
+
Sub-Chandra mass
helium igniters
−
1. At ~1051 ergs
1. Difficult to reach
MCh
2. 56Ni decay
powers
2. For MWD ≳
lightcurve
1.2M☉ collapse
to NS rather than
3. X; (Vj) consistent
explosion may
with spectra
ensue
4. MCh explains
homogeneity
Indirect double detonation or
“edge lit” detonation
One detonation propagates
outward (through He), inward
pressure wave compresses the
C-O, ignites off center, followed
by outward detonation.
At what mass does the WD explode?
Composition of high velocity ejecta
In sub-Chandra mass WDs
Intermediate mass elements sandwiched by Ni and He/Ni rich
High velocity Ni, He! No high velocity C!
For progenitors we have two
possible scenarios
Double degenerate
Merger of two CO WDs
brought together by
gravitational radiation
Single degenerate
A CO WD accretes material
from a main sequence or
red giant companion
Binary WD systems
Systems such as:
Recurrent novae
Supersoft x-ray sources
Symbiotic systems
Evolutionary Scenarios
Double degenerate scenario
Strengths
1.
2.
3.
4.
Population synthesis predicts the
right statistics.
Double degenerate systems
detected observationally.
Mergers with some significant
consequences appear inevitable.
In ellipticals, consistent with
observed x-ray flux (~30x smaller
than predicted for SDS).
Weaknesses
1.
Off-center carbon
ignition may lead to ONe-Mg WD and
accretion induced
collapse rather than
SN Ia.
Double degenerate scenario
1. The merger of two 0.9 M☉
WDs produced a
subluminous SN Ia (SN
1991bg-like).
Double degenerate scenario
2. Simulation of 0.6 M☉ +
0.9 M☉ suggested that
SNe Ia could be obtained if
 J  
Single degenerate scenario
Strengths
1.
2.
If accreted matter can be
retained, natural path to
increasing mass.
Candidate progenitors exist.
Weaknesses
1. It is not absolutely clear that a
hydrogen-accreting WD can
indeed reach MCh.
2. Limits on the presence of H
exclude symbiotics with the
highest mass loss rates.
3. In ellipticals, the observed x-ray
flux ~30x smaller than
predicted.
A few recent observational findings
1. Two populations:
“Prompt” – SN Ia rate ~ star
formation rate
“Delayed” – SN Ia rate ~ stellar
mass
⇓
a. Rate higher in late type
galaxies.
b. For higher z prompt
dominate sample.
c. Prompt are brighter.
Recent observational findings
2. A decrease with redshift in the strength of intermediate
mass element features (consistent with higher brightness,
which implies
larger mass
of 56Ni).
Recent observational findings
3. The luminosity-weighted age of the host galaxy is correlated
with the 56Ni yield ⇒ more massive progenitors give
rise to more
luminous
explosions.
Recent observational findings
4. Super-Chandrasekhar
mass progenitors?
E.g. SNLS-03D3bb
SN 2009dc.
Serendipity and SNe Ia
A short (10 sec) acquisition image by STIS on board HST
of the nucleus of the radio-loud galaxy 3C 78 revealed a
point source superposed very near the jet – a SN Ia.
Possibility to Increase SNe Ia Rate?
The shocks produced by jets can either:
a.
b.
Heat mass-donor star in binaries containing white dwarfs,
thereby increasing the mass transfer rate.
or
Compress clumps in the interstellar medium thereby increasing
the mass accretion rate onto low-velocity white dwarfs.
Prediction: The rate of classical novae should increase too,
because novae are obtained when white dwarfs accrete at
rates
Serendipity and Classical Novae
An HST program intended to
measure the proper motion of
the optical jet in M87
discovered 11 transient sources
in the vicinity of the jet.
HST WFPC2
Conclusions
1. Single degenerate scenario could, in principle, explain
everything: prompt are caused by accretion from young
main sequence stars (~8M☉),
and delayed are caused by
accretion from red giant
companions (~1M☉).
However, models involve
maybe too many “moving
parts.”
Conclusions
2. Double degenerates could perhaps produce SNe Ia,
especially in ellipticals, but many uncertainties remain.
3. Is there something to be learned from gamma-ray bursts?
In particular, if indeed both double degenerates and single
degenerates contribute to SNe Ia, then it would be hard to
believe that mergers and accretion from a red giant, in
ellipticals, would appear precisely the same in all twoparameter diagrams (e.g., the separation between long and
short GRBs in duration-hardness diagrams).
Consequently, there should be some phase space in which
the two progenitor families should separate.