HELIUM-IGNITED VIOLENT MERGERS AS A UNIFIED MODEL FOR NORMAL AND RAPIDLY DECLINING TYPE Ia SUPERNOVAE

The progenitors of Type Ia supernovae (SNe Ia) are still unknown, despite significant progress during the past several years in theory and observations. Violent mergers of two carbon–oxygen (CO) white dwarfs (WDs) are a candidate scenario suggested to be responsible for at least a significant fraction of normal SNe Ia. Here, we simulate the merger of two CO WDs using a moving-mesh code that allows for the inclusion of thin helium (He) shells (0.01 M☉) on top of the WDs at an unprecedented numerical resolution. The accretion of He onto the primary WD leads to the formation of a detonation in its He shell. This detonation propagates around the CO WD and sends a converging shock wave into its core, known to robustly trigger a second detonation, as in the well-known double-detonation scenario for He-accreting CO WDs. However, in contrast to that scenario where a massive He shell is required to form a detonation through thermal instability, here the He detonation is ignited dynamically. Accordingly the required He-shell mass is significantly smaller, and hence its burning products are unlikely to affect the optical display of the explosion. We show that this scenario, which works for CO primary WDs with CO- as well as He-WD companions, has the potential to explain the different brightness distributions, delay times, and relative rates of normal and fast declining SNe Ia. Finally, we discuss extensions to our unified merger model needed to obtain a comprehensive picture of the full observed diversity of SNe Ia.

[1]  Emilio Molina,et al.  Summary and Discussion , 2014 .

[2]  P. Nugent,et al.  'Super-Chandrasekhar' Type Ia Supernovae at nebular epochs , 2013, 1304.4952.

[3]  S. Woosley,et al.  MULTI-DIMENSIONAL MODELS FOR DOUBLE DETONATION IN SUB-CHANDRASEKHAR MASS WHITE DWARFS , 2013, 1303.0324.

[4]  W. Hillebrandt,et al.  3D deflagration simulations leaving bound remnants: a model for 2002cx-like Type Ia supernovae , 2012, 1210.5243.

[5]  W. Hillebrandt,et al.  On the brightness distribution of type Ia supernovae from violent white dwarf mergers , 2012, 1209.0645.

[6]  N. Soker,et al.  Explaining the Type Ia supernova PTF 11kx with a violent prompt merger scenario , 2012, 1207.5770.

[7]  P. Garnavich,et al.  NO STRIPPED HYDROGEN IN THE NEBULAR SPECTRA OF NEARBY TYPE Ia SUPERNOVA 2011fe , 2012, 1210.3027.

[8]  P. Mazzali,et al.  Spectral modelling of the ‘super-Chandrasekhar’ Type Ia SN 2009dc – testing a 2 M⊙ white dwarf explosion model and alternatives , 2012, 1209.1339.

[9]  M. Sullivan,et al.  PTF 11kx: A Type Ia Supernova with a Symbiotic Nova Progenitor , 2012, Science.

[10]  W. Hillebrandt,et al.  Stellar GADGET: a smoothed particle hydrodynamics code for stellar astrophysics and its application to Type Ia supernovae from white dwarf mergers , 2012, 1205.5806.

[11]  C. Tao,et al.  CONSTRAINING TYPE Ia SUPERNOVA MODELS: SN 2011fe AS A TEST CASE , 2012, 1203.4839.

[12]  R. Kirshner,et al.  THE LOW-VELOCITY, RAPIDLY FADING TYPE Ia SUPERNOVA 2002es , 2012, 1202.3140.

[13]  W. Hillebrandt,et al.  NORMAL TYPE Ia SUPERNOVAE FROM VIOLENT MERGERS OF WHITE DWARF BINARIES , 2012, 1201.5123.

[14]  Bradley E. Schaefer,et al.  An absence of ex-companion stars in the type Ia supernova remnant SNR 0509−67.5 , 2012, Nature.

[15]  Gabriel Rockefeller,et al.  REMNANTS OF BINARY WHITE DWARF MERGERS , 2011, 1112.1420.

[16]  Nathaniel R. Butler,et al.  Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe , 2011, Nature.

[17]  Nathaniel R. Butler,et al.  A COMPACT DEGENERATE PRIMARY-STAR PROGENITOR OF SN 2011fe , 2011, 1111.0966.

[18]  Rollin C. Thomas,et al.  PTF10ops – a subluminous, normal-width light curve Type Ia supernova in the middle of nowhere , 2011, 1108.0416.

[19]  R. Nichol,et al.  IMPROVED CONSTRAINTS ON TYPE Ia SUPERNOVA HOST GALAXY PROPERTIES USING MULTI-WAVELENGTH PHOTOMETRY AND THEIR CORRELATIONS WITH SUPERNOVA PROPERTIES , 2011, 1107.6003.

[20]  Enrico Ramirez-Ruiz,et al.  PRELUDE TO A DOUBLE DEGENERATE MERGER: THE ONSET OF MASS TRANSFER AND ITS IMPACT ON GRAVITATIONAL WAVES AND SURFACE DETONATIONS , 2011, 1101.5132.

[21]  J. Sollerman,et al.  High luminosity, slow ejecta and persistent carbon lines: SN 2009dc challenges thermonuclear explosion scenarios , 2010, 1011.5665.

[22]  I. Hook,et al.  SUBLUMINOUS TYPE Ia SUPERNOVAE AT HIGH REDSHIFT FROM THE SUPERNOVA LEGACY SURVEY , 2010, 1011.4531.

[23]  Chris L. Fryer,et al.  Delay times and rates for type Ia supernovae and thermonuclear explosions from double-detonation sub-Chandrasekhar mass models , 2010, 1011.1407.

[24]  W. Hillebrandt,et al.  DOUBLE-DETONATION SUB-CHANDRASEKHAR SUPERNOVAE: SYNTHETIC OBSERVABLES FOR MINIMUM HELIUM SHELL MASS MODELS , 2010, 1006.4489.

[25]  W. Hillebrandt,et al.  DETONATIONS IN SUB-CHANDRASEKHAR-MASS C+O WHITE DWARFS , 2010, 1003.2917.

[26]  D. Vanbeveren,et al.  The delay-time distribution of Type Ia supernovae: a comparison between theory and observation , 2010, 1003.2491.

[27]  D. Kasen,et al.  THERMONUCLEAR.Ia SUPERNOVAE FROM HELIUM SHELL DETONATIONS: EXPLOSION MODELS AND OBSERVABLES , 2010, 1002.2258.

[28]  W. Hillebrandt,et al.  Double-detonation sub-Chandrasekhar supernovae: can minimum helium shell masses detonate the core? , 2010, 1002.2173.

[29]  W. Hillebrandt,et al.  Sub-luminous type Ia supernovae from the mergers of equal-mass white dwarfs with mass ∼0.9M⊙ , 2009, Nature.

[30]  V. Springel.  E pur si muove: Galilean-invariant cosmological hydrodynamical simulations on a moving mesh , 2009, 0901.4107.

[31]  Jacobs University Bremen,et al.  SURFACE DETONATIONS IN DOUBLE DEGENERATE BINARY SYSTEMS TRIGGERED BY ACCRETION STREAM INSTABILITIES , 2009, 0911.0416.

[32]  M. Stritzinger,et al.  THE FAST DECLINING TYPE Ia SUPERNOVA 2003gs, AND EVIDENCE FOR A SIGNIFICANT DISPERSION IN NEAR-INFRARED ABSOLUTE MAGNITUDES OF FAST DECLINERS AT MAXIMUM LIGHT , 2009, 0908.1918.

[33]  Chris L. Fryer,et al.  RATES AND DELAY TIMES OF TYPE Ia SUPERNOVAE , 2009, 0904.3108.

[34]  Armin Rest,et al.  CfA3: 185 TYPE Ia SUPERNOVA LIGHT CURVES FROM THE CfA , 2009, 0901.4787.

[35]  D. Lamb,et al.  SPONTANEOUS INITIATION OF DETONATIONS IN WHITE DWARF ENVIRONMENTS: DETERMINATION OF CRITICAL SIZES , 2009, 0901.3677.

[36]  Zhanwen Han,et al.  The single degenerate channel for the progenitors of Type Ia supernovae , 2008, Proceedings of the International Astronomical Union.

[37]  S. E. Persson,et al.  The underluminous Type Ia supernova 2005bl and the class of objects similar to SN 1991bg , 2007, 0711.4548.

[38]  W. Hillebrandt,et al.  Double-detonation supernovae of sub-Chandrasekhar mass white dwarfs , 2007, 0710.5486.

[39]  P. Chandra,et al.  Detection of Circumstellar Material in a Normal Type Ia Supernova , 2007, Science.

[40]  Gijs Nelemans,et al.  Faint Thermonuclear Supernovae from AM Canum Venaticorum Binaries , 2007, astro-ph/0703578.

[41]  P. Mazzali,et al.  A Common Explosion Mechanism for Type Ia Supernovae , 2007, Science.

[42]  S. E. Persson,et al.  The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations? , 2006, astro-ph/0611295.

[43]  Douglas C. Leonard,et al.  Constraining the Type Ia Supernova Progenitor: The Search for Hydrogen in Nebular Spectra , 2006, 0710.3166.

[44]  Warren R. Brown,et al.  UBVRI Light Curves of 44 Type Ia Supernovae , 2005, astro-ph/0509234.

[45]  V. Springel.  The Cosmological simulation code GADGET-2 , 2005, astro-ph/0505010.

[46]  M. Livio,et al.  Have the Elusive Progenitors of Type Ia Supernovae Been Discovered? , 2003, astro-ph/0308018.

[47]  Adam Burrows,et al.  Type Ia Supernova Explosions in Binary Systems: The Impact on the Secondary Star and Its Consequences , 1999, astro-ph/9908116.

[48]  R. Schommer,et al.  The Reddening-Free Decline Rate Versus Luminosity Relationship for Type Ia Supernovae , 1999, astro-ph/9907052.

[49]  A. V. Tutukov,et al.  On the evolution of close binaries with components of initial mass between 3 solar masses and 12 solar masses , 1985 .