A theoretical color-velocity correlation for supernovae associated with gamma-ray bursts

TL;DR

This paper presents multi-dimensional radiative transfer models of supernovae with bipolar outflows, predicting orientation-dependent spectral and light curve features, including a correlation between line velocity and color that aids in identifying jet-driven supernovae.

Contribution

It introduces the first multi-dimensional radiative transfer calculations for aspherical supernova models, revealing orientation-dependent observable features and a consistent line velocity-color correlation.

Findings

Spectral and light curve features vary systematically with observer orientation.

Early phase light curves are brighter and bluer near the polar axis.

A consistent correlation between line velocity and color is predicted.

Abstract

We carry out the first multi-dimensional radiative transfer calculations to simultaneously compute synthetic spectra and light curves for models of supernovae driven by fast bipolar outflows. These allow us to make self-consistent predictions for the orientation dependence of both colour evolution and spectral features. We compare models with different degrees of asphericity and metallicity and find significant observable consequences of both. In aspherical models, we find spectral and light curve features that vary systematically with observer orientation. In particular, we find that the early phase light curves are brighter and bluer when viewed close to the polar axis but that the peak flux is highest for equatorial (off-axis) inclinations. Spectral line features also depend systematically on observer orientation, including the velocity of the SiII 6355A line. Consequently, our models predict a correlation between line velocity and color that could assist the identification of supernovae associated with off-axis jet-driven explosions. The amplitude and range of this correlation depends on the degree of asphericity, the metallicity and the epoch of observation but we find that it is always present and acts in the same direction.