Progenitors of SNe Ia

We are now relatively certain that the thermonuclear explosion of a white dwarf (WD) will produce a Type Ia supernova (SN Ia). Astrophysicists are, however, divided on the identity of the WD’s binary companion: is it another WD or a larger, non-degenerate star? Below I describe a recent paper that utilized the rare collection of extremely late-time photometric imaging of Type Ia SN, 2013aa in order to probe the unknown progenitors of the class as a whole.

Figure 1

SN 2013aa is a nearby SN Ia in host galaxy NGC 5643. The SN is highlighted by red lines to the left in a false-color RGB image using the Swift space telescope.

Figure 2

Using Hubble Space Telescope (HST) images of SN 2013aa, we detected the source at over 1500 days after the explosion’s maximum light. In the right figure, a Gemini explosion image of SN 2013aa (top left panel) is compared to an HST image at ~1500 days since explosion (bottom left panel). Only performed on four other SNe Ia, this detection of SN 2013aa marks the second latest photometric detection of a SN Ia to date.

Figure 3

By examining the supernova’s luminosity decline with respect to time, we calculated the abundances of radioactive decay elements (Co-56, Co-57 and Fe-55), all of which power the explosion at very late-times. Models of the radioactive decay powered light curve shown to the left. Each fit is dependent on the physics of the explosion and the total masses of radioactive decay elements produced.

Figure 4

We then compared the relative masses of these elements to those predicted in different 3-D explosion models for SNe Ia, which tentatively indicated a consistency between SN 2013aa and a double white dwarf progenitor system. However, as shown in Figure 4, explosion models for SNe Ia are wide ranging; we are in need of better observations of nearby SNe Ia combined with detailed modeling that can predict explosion observables.