Afterglows of Mildly Relativistic Supernovae: Baryon Loaded Blastwaves

TL;DR

This paper models the radio afterglows of mildly relativistic supernovae with baryon-loaded ejecta, explaining observations of SN 2009bb as a decelerating, massive relativistic shell driven by a central engine.

Contribution

It introduces a model for mildly relativistic supernovae with baryon-loaded outflows, extending afterglow analysis beyond ultra-relativistic regimes.

Findings

The model explains the radio evolution of SN 2009bb.

SN 2009bb had a highly baryon loaded, mildly relativistic outflow.

The dynamics are consistent with a decelerating relativistic shell.

Abstract

Relativistic supernovae have been discovered until recently only through their association with long duration Gamma Ray Bursts (GRB). As the ejecta mass is negligible in comparison to the swept up mass, the blastwaves of such explosions are well described by the Blandford-McKee (in the ultra relativistic regime) and Sedov-Taylor (in the non-relativistic regime) solutions during their afterglows. However, the recent discovery of the relativistic supernova SN 2009bb, without a detected GRB, has indicated the possibility of highly baryon loaded mildly relativistic outflows which remains in nearly free expansion phase during the radio afterglow. In this work, we consider the dynamics and emission from a massive, relativistic shell, launched by a Central Engine Driven EXplosion (CEDEX), decelerating adiabatically due to its collision with the pre-explosion circumstellar wind profile of the progenitor. We show that this model explains the observed radio evolution of the prototypical SN 2009bb and demonstrate that SN 2009bb had a highly baryon loaded, mildly relativistic outflow.