Shadows at Night, and Exposed to the Light: Type-Ia Supernova Classification Using Gamma-Ray Light Curves

Gamma rays have been understood to be an excellent diagnostic of SNeIa for nearly five decades. Critical diagnostic evidence supporting a specific thermonuclear scenario, or the identification of multiple evolutionary pathways, will transform our understanding of the role SNeIa play throughout the cosmos, including as cosmological probes. The temporal evolution of emergent nuclear gamma rays is a valuable diagnostic tool with which to probe SNeIa, the “beacons of the cosmos”. Discrete energy nuclear gamma-ray lines emerge from optically thin regions, and continuum photons emerge from more opaque ones during extended post-explosion epochs. We describe a phenomenological approach to characterizes the temporal and spectral evolution of the emergent nuclear emission from SNeIa. Gamma-ray light-curve shapes are simple, and this simplicity means that their defining features can be encapsulated in a straightforward parameterization. The parameters that characterize nuclear light-curves are a phenomenological descriptor of emergent nuclear emission properties; individual supernova descriptors within the dataspace defined by these parameters can subsequently be connected to thermonuclear scenarios and progenitor models. The parameterization approach, nuclear classification methodology, and likelihood-based connections between identified phenomenological subclasses and thermonuclear scenarios are discussed.