Optical Observations of the 2002cx-like Supernova 2014ek, and Characterizations of SNe Iax

TL;DR

This paper presents optical observations of SN 2014ek, a supernova similar to SN 2002cx-like events, analyzing its properties, spectral features, and host galaxy environment, and comparing it with other SNe Iax.

Contribution

It provides detailed observational data on SN 2014ek and a comprehensive analysis of SNe Iax, including their spectral characteristics, explosion parameters, and host galaxy environments, expanding understanding of this supernova subclass.

Findings

SN 2014ek is underluminous with a peak magnitude of -17.66 mag.

Ejecta velocity near maximum light is about 5000 km/s, half that of normal SNe Ia.

SNe Iax tend to occur in late-type, star-forming regions, indicating young progenitors.

Abstract

We present optical observations of supernova (SN) 2014ek discovered during the Tsinghua-NAOC Transient Survey (TNTS), which shows properties that are consistent with those of SN 2002cx-like events (dubbed as SNe Iax). The photometry indicates that it is underluminous compared to normal SNe Ia, with the absolute $V$-band peak magnitude being as $-17.66\pm0.20$ mag. The spectra are characterized by highly ionized Fe III and intermediate-mass elements (IMEs). The expansion velocity of the ejecta is found to be $\sim$5000 km s$^{-1}$ near the maximum light, only half of that measured for normal SNe Ia. The overall spectral evolution is quite similar to SN 2002cx and SN 2005hk, while the absorption features of the main IMEs seem to be relatively weaker. The ${}^{56}$Ni mass synthesized in the explosion is estimated to be about 0.08 M$_{\odot}$ from the pseudo bolometric light curve. Based on a large sample of SNe Iax, we examined the relations between peak luminosity, ejecta velocity, decline rate, and peak $V - R$ color but did not find noticeable correlations between these observables, in particular when a few extreme events like SN 2008ha are excluded in the analysis. For this sample, we also studied the birthplace environments and confirm that they still hold the trend of occurring preferentially in late-type spiral galaxies. Moreover, SNe Iax tend to occur in large star-forming regions of their host galaxies, more similar to SNe Ibc than SNe II, favoring that their progenitors should be associated with very young stellar populations.