Rapidly-Declining Hostless Type Ia Supernova KSP-OT-201509b from the KMTNet Supernova Program: Transitional Nature and Constraint on ${}^{56}$Ni Distribution and Progenitor Type

Abstract

We report the early discovery and multi-color ($BVI$) high-cadence light curve analyses of a rapidly-declining sub-Chandrasekhar Type Ia supernova KSP-OT-201509b (= AT2015cx) from the KMTNet Supernova Program. The Phillips parameter and color stretch parameter of KSP-OT-201509b (= AT2015cx) are $\Delta$$M_{B,15}$ $\simeq$ 1.62 mag and $s_{BV}$ $\simeq$ 0.54, respectively, at an inferred redshift of 0.072. These, together with other measured parameters (such as the strength of the secondary $I$-band peak, colors and luminosity), identify the source to be a rapidly-declining Type Ia of transitional nature that is closer to Branch Normal than 91bg-like. Its early light curve evolution and bolometric luminosity are consistent with those of homologously expanding ejecta powered by radioactive decay and a Type Ia SN explosion with 0.32 $\pm$ 0.01 $M_{\odot }$ of synthesized ${}^{56}$Ni mass, 0.84 $\pm$ 0.12 $M_{\odot }$ of ejecta mass and (0.61 $\pm$ 0.14) $\times$ 10${}^{51}$ erg of ejecta kinetic energy. While its $B-V$ and $V-I$ colors evolve largely synchronously with the changes in the $I$-band light curve as found in other supernovae, we also find the presence of an early redward evolution in $V-I$ prior to --10 days since peak. The bolometric light curve of the source is compatible with a stratified ${}^{56}$Ni distribution extended to shallow layers of the exploding progenitor. Comparisons between the observed light curves and those predicted from ejecta-companion interactions clearly disfavor Roche Lobe-filling companion stars at large separation distances, thus supporting a double-degenerate scenario for its origin. The lack of any apparent host galaxy in our deep stack images reaching a sensitivity limit of $\sim$ 28 $\mathrm{mag}\mathrm{arcse}{\mathrm{c}}^{-2}$ makes KSP-OT-201509b a hostless Type Ia supernova and offers new insights into supernova host galaxy environments.

39 pages, 20 figures, To appear in ApJ

References in corpus (27)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Rates and properties of type Ia supernovae as a function of mass and star-formation in their host galaxies
• A Common Explosion Mechanism for Type Ia Supernovae
• Double-detonation sub-Chandrasekhar supernovae: synthetic observables for minimum helium shell mass models
• Secondary Maximum in the Near-Infrared Lightcurves of Type Ia Supernovae
• SiFTO: An Empirical Method for Fitting SNe Ia Light Curves
• The Broad-lined Type Ic SN 2003jd
• The Carnegie Supernova Project: Intrinsic Colors of Type Ia Supernovae
• The underluminous Type Ia Supernova 2005bl and the class of objects similar to SN 1991bg
• Early Blue Excess from the Type Ia Supernova 2017cbv and Implications for Its Progenitor
• A New Method to Calibrate the Magnitudes of Type Ia Supernovae at Maximum Light
• Evidence for sub-Chandrasekhar-mass progenitors of Type Ia supernovae at the faint end of the width-luminosity relation
• Double Detonations with Thin, Modestly Enriched Helium Layers Can Make Normal Type Ia Supernovae
• Light and color curve properties of type Ia supernovae: Theory vs. Observations
• Inside the whale: the structure and dynamics of the isolated Cetus dwarf spheroidal
• Two New Calcium-Rich Gap Transients in Group and Cluster Environments
• Constraints on the origin of the first light from SN2014J
• Determining the ${}^{56}$Ni distribution of type Ia supernovae from observations within days of explosion
• Abundance stratification in Type Ia supernovae - V. SN 1986G bridging the gap between normal and subluminous SNe Ia
• Dwarf Galaxy Discoveries from the KMTNet Supernova Program I. The NGC 2784 Galaxy Group
• Evidence for Sub-Chandrasekhar Mass Type Ia Supernovae from an Extensive Survey of Radiative Transfer Models
• Deep spectroscopic luminosity function of Abell 85: no evidence for a steep upturn of the faint-end slope
• Near-infrared light curves of Type Ia supernovae: Studying the properties of the second maximum
• Confirmation of Hostless Type Ia Supernovae Using Hubble Space Telescope Imaging
• SN 2015bp: adding to the growing population of transitional type Ia supernovae
• Dwarf Galaxy Discoveries from the KMTNet Supernova Program II. The NGC 3585 Group and Its Dynamical State
• Beacons In the Dark: Using Novae and Supernovae to Detect Dwarf Galaxies in the Local Universe

Cited by in corpus (2)

• Infant-phase reddening by surface Fe-peak elements in a normal Type Ia Supernova
• Discovery of a Short-Period and Unusually Helium-Deficient Dwarf Nova KSP-OT-201701a by the KMTNet Supernova Program