The High-Metallicity Explosion Environment of the Relativistic Supernova 2009bb

TL;DR

This study examines the high-metallicity environment of supernova 2009bb, which produced a relativistic outflow without an associated gamma-ray burst, challenging previous assumptions about the environments necessary for such phenomena.

Contribution

It provides the first detailed environmental analysis of SN 2009bb, revealing high metallicity in its host environment, contrasting with typical gamma-ray burst hosts and informing models of relativistic supernovae.

Findings

SN 2009bb's environment has ~2x solar metallicity.

The host environment differs from typical LGRB hosts.

Relativistic supernovae can occur in high-metallicity environments.

Abstract

We investigate the environment of the nearby (d ~ 40Mpc) broad-lined Type Ic supernova SN 2009bb. This event was observed to produce a relativistic outflow likely powered by a central accreting compact object. While such a phenomenon was previously observed only in long-duration gamma-ray bursts (LGRBs), no LGRB was detected in association with SN 2009bb. Using an optical spectrum of the SN 2009bb explosion site, we determine a variety of ISM properties for the host environment, including metallicity, young stellar population age, and star formation rate. We compare the SN explosion site properties to observations of LGRB and broad-lined SN Ic host environments on optical emission line ratio diagnostic diagrams. Based on these analyses, we find that the SN 2009bb explosion site has a very high metallicity of ~2x solar, in agreement with other broad-lined SN Ic host environments and at odds with the low-redshift LGRB host environments and recently proposed maximum metallicity limits for relativistic explosions. We consider the implications of these findings and the impact that SN 2009bb's unusual explosive properties and environment have on our understanding of the key physical ingredient that enables some SNe to produce a relativistic outflow.