title: The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star.
abstract: The accelerating expansion of the Universe, and the need for dark energy, were inferred from observations of type Ia supernovae. There is a consensus that type Ia supernovae are thermonuclear explosions that destroy carbon-oxygen white dwarf stars that have accreted matter from a companion star, although the nature of this companion remains uncertain. These supernovae are thought to be reliable distance indicators because they have a standard amount of fuel and a uniform trigger: they are predicted to explode when the mass of the white dwarf nears the Chandrasekhar mass of 1.4 solar masses (M(o)). Here we show that the high-redshift supernova SNLS-03D3bb has an exceptionally high luminosity and low kinetic energy that both imply a super-Chandrasekhar-mass progenitor. Super-Chandrasekhar-mass supernovae should occur preferentially in a young stellar population, so this may provide an explanation for the observed trend that overluminous type Ia supernovae occur only in 'young' environments. As this supernova does not obey the relations that allow type Ia supernovae to be calibrated as standard candles, and as no counterparts have been found at low redshift, future cosmology studies will have to consider possible contamination from such events.
authors.affiliation: Department of Astronomy and Astrophysics, University of Toronto, 60 St George Street, Toronto, Ontario M5S 3H8, Canada. howell@astro.utoronto.ca
authors.forename: D Andrew
authors.initials: DA
authors.lastname: Howell
authors.forename: Mark
authors.initials: M
authors.lastname: Sullivan
authors.forename: Peter E
authors.initials: PE
authors.lastname: Nugent
authors.forename: Richard S
authors.initials: RS
authors.lastname: Ellis
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Conley
authors.forename: Damien
authors.initials: D
authors.lastname: Le Borgne
authors.forename: Raymond G
authors.initials: RG
authors.lastname: Carlberg
authors.forename: Julien
authors.initials: J
authors.lastname: Guy
authors.forename: David
authors.initials: D
authors.lastname: Balam
authors.forename: Stephane
authors.initials: S
authors.lastname: Basa
authors.forename: Dominique
authors.initials: D
authors.lastname: Fouchez
authors.forename: Isobel M
authors.initials: IM
authors.lastname: Hook
authors.forename: Eric Y
authors.initials: EY
authors.lastname: Hsiao
authors.forename: James D
authors.initials: JD
authors.lastname: Neill
authors.forename: Reynald
authors.initials: R
authors.lastname: Pain
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Perrett
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Pritchet