SN 2002cx: The Most Peculiar Known Type Ia Supernova

Abstract

We present photometric and spectroscopic observations of supernova (SN) 2002cx, which reveal it to be unique among all observed type Ia supernovae (SNe Ia). SN 2002cx exhibits a SN 1991T-like premaximum spectrum, a SN 1991bg-like luminosity, and expansion velocities roughly half those of normal SNe Ia. Photometrically, SN 2002cx has a broad peak in the $R$ band and a plateau phase in the $I$ band, and slow late-time decline. The $(B - V)$ color evolution is nearly normal, but the $(V - R)$ and $(V - I)$ colors are very red. Early-time spectra of SN 2002cx evolve very quickly and are dominated by lines from Fe-group elements; features from intermediate-mass elements (Ca, S, Si) are weak or absent. Mysterious emission lines are observed around 7000 \AA\ at about 3 weeks after maximum brightness. The nebular spectrum of SN 2002cx is also unique, consisting of narrow iron and cobalt lines. The observations of SN 2002cx are inconsistent with the observed spectral/photometric sequence, and provide a major challenge to our understanding of SNe Ia. No existing theoretical model can successfully explain all observed aspects of SN 2002cx.Comment: 60 pages, 12 figures. A high resolution PostScript version is available at http://astro.berkeley.edu/~weidong/sn2002cx.p

Nuclear Dominated Accretion Flows in Two Dimensions. I. Torus Evolution With Parametric Microphysics

“…He was motivated by the recent discovery of several Type I supernovae which are dimmer and/or more rapidly evolving than normal SNe Ia or Ib/c (e.g., Li et al 2003;Jha et al 2006;Foley et al 2009;Perets et al 2010;Waldman et al 2011;Kasliwal et al 2012). The rapid evolution and low luminosities of these events require both a lower 56 Ni yield and lower total ejecta mass than values characteristic of normal SNe.…”

“…One type of SNe with characteristics seemingly compatible with those resulting from a WD-NS/BH merger are the events prototyped by SN 2002cx and SN 2005bj ("SN 2002cx-like" events;Li et al 2003;Jha et al 2006;Phillips et al 2007;Foley et al 2009). This rare class of Ia SNe is in part distinguished by the following features: (1) high ionization spectrum at maximum light, and the presence of elements lighter than the Fe group at all epochs, both indicating that the ejecta is extensively mixed; (2) a low peak luminosity compared to that expected given its rate of decline (i.e., not following the standard "Phillips relation"), indicating a wide range of synthesized 56 Ni mass, ranging from M Ni ∼ 3 × 10 −3 -0.2 M ; (3) low expansion velocities ∼3000-5000 km s −1 (hence low kinetic energy) compared to a normal SN Ia (∼10,000 km s −1 ); (4) permitted Fe ii lines and continuum photospheric emission at late times, indicating very low velocities 1000 km s −1 for the innermost ejecta; and (5) host galaxies with both active star formation (Foley et al 2009) as well as older stellar populations (Foley et al 2010).…”

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“…Branch 2001;Nomoto et al 2003;Li et al 2003). This leaves concerns about applying Phillips' relation to very distant SNe Ia.…”

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“…It is spectroscopically like SN 1991bg, a sub-luminous event, but photometrically like SN 1991T, the classic super-luminous SN Ia (Li et al 2003). Fig.…”