SNLS-03D3bb
Andy Howell
University of Toronto
and the Supernova Legacy Survey
(SNLS)
Host
HST
z = 0.2440
From PEGASE 2
fits to host ugriz
photometry:
CFHT
0.81
log M gal  8.930.50
 0.02
SFR  1.26 1
M yr-1
 Formally implies host age of 0.7 Gyr, though highly uncertain
0.81
log M gal  8.930.50
CFHT
Si II velocity
Low-z data from Benetti et al. 2005
Lightcurve
V=20.5 ± 0.06
MV = -19.94 ±
0.06
Use only r, i fit
s = 1.13
Sparse LC
from early
days of survey
V magnitude distribution
MV = -19.94 ± 0.06
2.2 times the
luminosity of
median SN Ia
Low-z
Astier et
al. sample
56Ni
mass
Arnett’s rule: Luminosity at maximum is
proportional to spontaneous energy
deposition by radioactive decay.
M Ni
L bol
=
α S (t r )
: ratio of bolometric to radioactivity luminosities
S
: energy per second per solar mass from
radioactive deacay
 = 6.3110 43 e  tr /8.8 +1.43 10 43 e  tr /111
erg s-1 M-1
S
Using tr = -19.5 (Conley et al. 2006),  = 1.2
(Nugent et al. 1996), get MNi = 1.29 ± 0.07 M
Velocity from kinetic energy
KE is nuclear energy
minus binding energy
v ke =
2 (E n  E b )
M
WD
3 kinds of elements: Fe-peak,
IME, unburned C/O
Energy from burning to Fe peak:
E Fe = 1.55  10
51
erg s-1 M-1
Burning to Si produces 76%
as much
E n = E Fe M W D (f Fe + 0.76 f IME )
56Ni
is 70% of Fe-peak elements:
M Ni  0 . 7 M WD f Fe
Binding energy (Yoon & Langer
2005)
- 1.4 M WD: 0.5e51 erg
- 2.0 M WD: 1.3e51 erg
Implications - Progenitors
• Double degenerate model: merger of
two massive WDs can produce superChandra product. In youngest
populations, only massive WDs exist.
Before 0.9 Gyr, combined WD mass
must be > Chandrasekhar mass.
• Single degenerate model: rapid rotation
could support 2 solar mass WD
according to Yoon & Langer 2005.
Young pop. favored for higher starting
WD, secondary masses.
Implications
• The most luminous SNe occur in young
populations
• Super-Chandra model predicts more
luminous SNe in younger populations
• Chandra model has no explanation for
this.
• Could WD mass partially drive
luminosity fluctuations in SNe Ia?
Conclusions - Observations
• MV=19.94 ± 0.06, brightest SN Ia ever
observed (with the possible exception of the
interacting SN 2002ic)
• SiII velocity at +2d among the lowest seen,
8000 km/s
• SiII strong relative to CaII at +2d, in contrast
with other SNe Ia
• CII near maximum implies the presence of
unburned material deep into the SN
• Low-mass, blue host implies a young
progenitor age
Conclusions - Interpretation
• Arnett’s law implies ~1.3 M 56Ni.
• If ~40% of elements are non-56Ni, MWD ~ 2.1 M
• High 56Ni mass implies large nuclear energy, which
should produce large velocities in Chandrasekhar
model.
• Low velocity consistent with increased binding energy
of super-Chandra model.
• Young galaxy consistent with expectations from
Super-Chandra model
• SNLS-03D3bb meets every expectation of the superChandra model
Conclusions - Cosmology
• WD mass may partially drive SN Ia luminosity
• SNLS-03D3bb does not follow stretchluminosity relationship (it is too bright by 4.4
sigma).
• “Evolution” in SNe with redshift?
• SNLS-03D3bb was thrown out of Astier et al.
(2006), but less extreme examples could be
in data set.