Optical Synchrotron Precursors of Radio Hypernovae

TL;DR

This paper explores optical and radio precursors of radio-bright hypernovae, suggesting they are powered by choked jets or magnetar winds, and discusses how optical precursors can help distinguish different explosion scenarios.

Contribution

It introduces a model linking radio-bright hypernovae to spherical explosions driven by jets or magnetar winds and predicts optical precursors observable before the supernova peak.

Findings

Radio-bright hypernovae can be powered by choked jets or magnetar winds.

Optical precursors of hypernovae can be observed days before the supernova peak.

Optical precursor brightness depends on the presence of additional trans-relativistic components.

Abstract

We examine the bright radio synchrotron counterparts of low-luminosity gamma-ray bursts (llGRBs) and relativistic supernovae (SNe) and find that they can be powered by spherical hypernova (HN) explosions. Our results imply that radio-bright HNe are driven by relativistic jets that are choked deep inside the progenitor stars or quasi-spherical magnetized winds from fast-rotating magnetars. We also consider the optical synchrotron counterparts of radio-bright HNe and show that they can be observed as precursors several days before the SN peak with an r-band absolute magnitude of M_r ~ -14 mag. While previous studies suggested that additional trans-relativistic components are required to power the bright radio emission, we find that they overestimated the energy budget of the trans-relativistic component by overlooking some factors related to the minimum energy of non-thermal electrons. If an additional trans-relativistic component exists, then a much brighter optical precursor with M_r ~ -20 mag can be expected. Thus, the scenarios of radio-bright HNe can be distinguished by using optical precursors, which can be detectable from < 100 Mpc by current SN surveys like the Kiso SN Survey, Palomar Transient Factory, and Panoramic Survey Telescope & Rapid Response System.