An Agnostic Approach to Building Empirical Type Ia Supernova Light Curves: Evidence for Intrinsic Chromatic Flux Variation Using Nearby Supernova Factory Data

TL;DR

This paper introduces a new empirical model for Type Ia supernova light curves that captures intrinsic chromatic flux variations without relying on dust extinction assumptions, revealing that about 13% of phase-independent flux variance is intrinsic.

Contribution

The paper presents a novel empirical SN Ia model with multiple phase-independent templates, avoiding dust assumptions and capturing intrinsic variability more accurately.

Findings

Approximately 13% of phase-independent flux variance is intrinsic.

The model distinguishes dust-like and intrinsic flux variations.

Previous models may conflate intrinsic variability with dust effects.

Abstract

We present a new empirical Type Ia supernova (SN Ia) model with three chromatic flux variation templates: one phase dependent and two phase independent. No underlying dust extinction model or patterns of intrinsic variability are assumed. Implemented with Stan and trained using spectrally binned Nearby Supernova Factory spectrophotometry, we examine this model's 2D, phase-independent flux variation space using two motivated basis representations. In both, the first phase-independent template captures variation that appears dust-like, while the second captures a combination of effectively intrinsic variability and second-order dust-like effects. We find that approximately 13% of the modeled phase-independent flux variance is not dust-like. Previous empirical SN Ia models either assume an effective dust extinction recipe in their architecture, or only allow for a single mode of phase-independent variation. The presented results demonstrate such an approach may be insufficient, because it could "leak" noticeable intrinsic variation into phase-independent templates.