Off-center explosions of Chandrasekhar-mass white dwarfs: an explanation of super-bright type Ia supernovae?

Free access article

Issue		A&A Volume 465, Number 2, April II 2007


Page(s)		L17 - L20
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20077100

A&A 465, L17-L20 (2007)
DOI: 10.1051/0004-6361:20077100

Letter

Off-center explosions of Chandrasekhar-mass white dwarfs: an explanation of super-bright type Ia supernovae?

W. Hillebrandt¹, S. A. Sim¹, and F. K. Röpke^{1, 2}

¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
e-mail: [wfh;ssim;fritz]@mpa-garching.mpg.de
² Department of Astronomy and Astrophysics, University of California, Santa Cruz, 1156 High Street, Santa Cruz CA 95064, USA

(Received 15 January 2007 / Accepted 13 February 2007)

Abstract
Context.The recent discovery of a very bright type Ia supernova, SNLS-03D3bb ( $\equiv$ SN 2003fg), in the Supernova Legacy Survey (SNLS) has raised the question of whether super-Chandrasekhar-mass white-dwarf stars are needed to explain such bright explosions. Progenitors of this sort could form by mergers of pairs of rather massive white dwarfs. Binary systems of two white dwarfs in close orbit, where their total mass significantly exceeds the Chandrasekhar mass, have not yet been found. Therefore SNLS-03D3bb could establish the first clear case of a double-degenerate progenitor of a (peculiar) type Ia supernovae. Moreover, if this interpretation is correct, it casts some doubt on the universality of the calibration relations used to make SNe Ia distance indicators for cosmology.
Aims.We aim to evaluate the case for a super-Chandrasekhar-mass progenitor for SNLS-03D3bb in light of previous theoretical work on super-Chandrasekhar-mass explosions. Furthermore, we propose an alternative scenario involving only a Chandrasekhar-mass progenitor.
Methods.We present a theoretically motivated critical discussion of the expected observational fingerprints of super-Chandrasekhar-mass explosions. As an alternative, we describe a simple class of aspherical Chandrasekhar-mass models in which the products of nuclear burning are displaced from the center. We then perform simple radiative transfer calculations to predict synthetic lightcurves for one such off-center explosion model.
Results.In important respects, the expected observational consequences of super-Chandrasekhar-mass explosions are not consistent with the observations of SNLS-03D3bb. We demonstrate that the lopsided explosion of a Chandrasekhar-mass white dwarf could provide a better explanation.

Key words: stars: supernovae: general -- stars: white dwarfs -- hydrodynamics -- methods: numerical

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