Can the violent merger of white dwarfs explain the slowest declining Type Ia supernova SN 2011aa?

TL;DR

This study investigates whether the slow decline of supernova SN 2011aa can be explained by a violent merger of white dwarfs, supported by observations and radiative transfer modeling.

Contribution

It demonstrates that the slow decline and large ejecta mass of SN 2011aa are consistent with a double degenerate, violent merger explosion model.

Findings

SN 2011aa has the slowest decline rate among SNe Ia.

The ejecta mass is estimated between 1.8 and 2.6 solar masses.

Synthetic spectra and light curves match the violent merger model.

Abstract

We present optical observations and Monte Carlo radiative transfer modeling of the Type Ia supernova SN 2011aa. With a $\Delta m_{15} (B)$ of $0.59 \pm 0.07$ mag and a peak magnitude $M_{\rm B}$ of $-19.30 \pm 0.27$ mag, SN 2011aa has the slowest decline rate among SNe Ia. The secondary maximum in the $I$-band is absent or equally bright as the primary maximum. The velocity of C II is lower than the velocity of Si II. This indicates either presence of C at lower velocities than Si or a line of sight effect. Application of Arnett's radiation diffusion model to the bolometric light curve indicates a massive ejecta $M_{\rm{ej}} ~ 1.8 - 2.6~M_{\odot}$. The slow decline rate and large ejecta mass, with a normal peak magnitude, are well explained by double degenerate, violent merger explosion model. The synthetic spectra and light curves generated with SEDONA considering a violent merger density profile match the observations.