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

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 $M_{\mathrm{B}}$ 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 $M_{\mathrm{ej}}1.8-2.6M_{\odot }$. 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.

12 pages, 4 figures, 1 table. Accepted for publication in Astrophysical Journal Letters