The evolution of the peculiar Type Ia supernova SN 2005hk over 400 days

TL;DR

This study presents detailed photometric and spectroscopic observations of the peculiar Type Ia supernova SN 2005hk over 400 days, revealing its underluminosity, low ejecta velocity, and spectral evolution, and models its explosion as a low-energy Chandrasekhar-mass thermonuclear event.

Contribution

It provides the first comprehensive long-term observational analysis of SN 2005hk, including spectral modeling and explosion energetics, highlighting its peculiarities compared to normal Type Ia supernovae.

Findings

SN 2005hk is underluminous and has lower ejecta velocity than normal Type Ia supernovae.

Spectra beyond 200 days lack forbidden lines, dominated by permitted lines with P-Cygni profiles.

A low-energy Chandrasekhar-mass explosion model explains the observed light curve and spectra.

Abstract

$UBVRI$ photometry and medium resolution optical spectroscopy of peculiar Type Ia supernova SN 2005hk are presented and analysed, covering the pre-maximum phase to around 400 days after explosion. The supernova is found to be underluminous compared to "normal" Type Ia supernovae. The photometric and spectroscopic evolution of SN 2005hk is remarkably similar to the peculiar Type Ia event SN 2002cx. The expansion velocity of the supernova ejecta is found to be lower than normal Type Ia events. The spectra obtained $\gsim 200$ days since explosion do not show the presence of forbidden [\ion{Fe}{ii}], [\ion{Fe}{iii}] and [\ion{Co}{iii}] lines, but are dominated by narrow, permitted \ion{Fe}{ii}, NIR \ion{Ca}{ii} and \ion{Na}{i} lines with P-Cygni profiles. Thermonuclear explosion model with Chandrasekhar mass ejecta and a kinetic energy smaller ($\KE = 0.3 \times 10^{51} {\rm ergs}$) than that of canonical Type Ia supernovae is found to well explain the observed bolometric light curve. The mass of \Nifs synthesized in this explosion is $0.18 \Msun$. The early spectra are successfully modeled with this less energetic model with some modifications of the abundance distribution. The late spectrum is explained as a combination of a photospheric component and a nebular component.