Comprehensive observations of the bright and energetic Type Iax SN 2012Z: Interpretation as a Chandrasekhar mass white dwarf explosion^{⋆,⋆⋆,⋆⋆⋆}

¹ Department of Physics and AstronomyAarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: max@phys.au.dk
² Las Cumbres Observatory Global Telescope Network, Inc. Santa Barbara, CA 93117, USA
³ Department of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara, CA 93106-9530, USA
⁴ Department of Physics, Florida State University, Tallahassee, FL 32306, USA
⁵ Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks, Rm 100, Norman, OK 73019-2061, USA
⁶ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁷ Carnegie Observatories, Las Campanas Observatory, Casilla 601 La Serena, Chile
⁸ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
⁹ Astronomy Department, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801, USA
¹⁰ Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
¹¹ Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA
¹² INAF-Osservatorio Astronomico di Padova, vicolo dell Osservatorio 5, 35122 Padova, Italy
¹³ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics & Astronomy, Texas A. & M. University, Department of Physics, 4242 Tamu, College Station, TX 77843, USA
¹⁴ Center for Mathematical Modelling, Universidad de Chile, Avenida Blanco Encalada 2120 Piso 7, Santiago, Chile
¹⁵ University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259, USA
¹⁶ Departamento Ciencias Fosicas, Universidad Andres Bello, Av. Republica 252, Santiago, Chile

Received: 9 May 2014
Accepted: 24 September 2014

Abstract

We present ultraviolet through near-infrared (NIR) broadband photometry, and visual-wavelength and NIR spectroscopy of the Type Iax supernova (SN) 2012Z. The data set consists of both early- and late-time observations, including the first late phase NIR spectrum obtained for a spectroscopically classified SN Iax. Simple model calculations of its bolometric light curve suggest SN 2012Z produced ~0.3 M_⊙ of ⁵⁶Ni, ejected about a Chandrasekhar mass of material, and had an explosion energy of ~10⁵¹ erg, making it one of the brightest (M_B = −18.3 mag) and most energetic SN Iax yet observed. The late phase (+269d) NIRspectrum of SN 2012Z is found to broadly resemble similar epoch spectra of normal SNe Ia; however, like other SNe Iax, corresponding visual-wavelength spectra differ substantially from all supernova types. Constraints from the distribution of intermediate mass elements, e.g., silicon and magnesium, indicate that the outer ejecta did not experience significant mixing during or after burning, and the late phase NIR line profiles suggests most of the ⁵⁶Ni is produced during high density burning. The various observational properties of SN 2012Z are found to be consistent with the theoretical expectations of a Chandrasekhar mass white dwarf progenitor that experiences a pulsational delayed detonation, which produced several tenths of a solar mass of ⁵⁶Ni during the deflagration burning phase and little (or no) ⁵⁶Ni during the detonation phase. Within this scenario only a moderate amount of Rayleigh-Taylor mixing occurs both during the deflagration and fallback phase of the pulsation, and the layered structure of the intermediate mass elements is a product of the subsequent denotation phase. The fact that the SNe Iax population does not follow a tight brightness-decline relation similar to SNe Ia can then be understood in the framework of variable amounts of mixing during pulsational rebound and variable amounts of ⁵⁶Ni production during the early subsonic phase of expansion.