Properties of the ultraviolet flux of type Ia supernovae: an analysis with synthetic spectra of SN 2001ep and SN 2001eh

TL;DR

This study investigates the ultraviolet spectral properties of Type Ia supernovae using HST data and synthetic spectral modeling, revealing how elemental abundances influence UV flux through reverse fluorescence.

Contribution

It introduces a detailed Monte Carlo spectral synthesis approach to analyze UV flux dependence on composition and density in supernova ejecta, challenging previous assumptions.

Findings

UV flux is largely formed by reverse fluorescence scattering.

Increased iron-group elements can enhance UV flux, contrary to prior beliefs.

Spectral models show the importance of ionization and line blocking effects.

Abstract

The spectral properties of type Ia supernovae in the ultraviolet (UV) are investigated using the early-time spectra of SN 2001ep and SN 2001eh obtained using the Hubble Space Telescope (HST). A series of spectral models is computed with a Monte Carlo spectral synthesis code, and the dependence of the UV flux on the elemental abundances and the density gradient in the outer layers of the ejecta is tested. A large fraction of the UV flux is formed by reverse fluorescence scattering of photons from red to blue wavelengths. This process, combined with ionization shifts due to enhanced line blocking, can lead to a stronger UV flux as the iron-group abundance in the outer layers is increased, contrary to previous claims.