Evidence for a pulsar wind nebula in the Type Ib-peculiar supernova SN 2012au

TL;DR

This study presents late-time optical and X-ray observations of supernova SN 2012au, providing evidence for a pulsar wind nebula influencing its explosion dynamics, and suggests a common late-phase evolution among diverse energetic supernovae.

Contribution

It offers the first late-time spectrum of SN 2012au and links its properties to pulsar/magnetar wind nebulae, expanding understanding of supernova explosion mechanisms.

Findings

Detection of forbidden oxygen and sulfur lines at 6.2 years post-explosion.

Absence of narrow H lines indicating minimal circumstellar interaction.

No X-ray emission detected, constraining the nebula's properties.

Abstract

We present an optical spectrum of the energetic Type Ib supernova (SN) 2012au obtained at an unprecedented epoch of 6.2 years after explosion. Forbidden transition emission lines of oxygen and sulfur are detected with expansion velocities of 2300 km/s. The lack of narrow H Balmer lines suggests that interaction with circumstellar material is not a dominant source of the observed late-time emission. We also present a deep Chandra observation that reveals no X-ray emission down to a luminosity of L_X < 2 x 10^{38} erg/s (0.5-10 keV). Our findings are consistent with the notion that SN 2012au is associated with a diverse subset of SNe, including long-duration gamma-ray burst SNe and superluminous SNe, harboring pulsar/magnetar wind nebulae that influence core-collapse explosion dynamics on a wide range of energy scales. We hypothesize that these systems may all evolve into a similar late-time phase dominated by forbidden oxygen transitions, and predict that emission line widths should remain constant or broaden a few per cent per year due to the acceleration of ejecta by the pulsar/magnetar bubble.