A surge of light at the birth of a supernova

TL;DR

This paper reports the serendipitous discovery of a supernova's early brightening, providing detailed insights into the progenitor's outer structure and shock physics through frequent observations and hydrodynamical modeling.

Contribution

It introduces detailed early-time observations of a supernova and develops hydrodynamical models that separate shock propagation from explosion mechanisms.

Findings

Rapid optical brightening of about 40 magnitudes per day observed

Detailed study of the progenitor's outer structure achieved

Hydrodynamical models successfully explain the supernova evolution

Abstract

It is difficult to establish the properties of massive stars that explode as supernovae. The electromagnetic emission during the first minutes to hours after the emergence of the shock from the stellar surface conveys important information about the final evolution and structure of the exploding star. However, the unpredictable nature of supernova events hinders the detection of this brief initial phase. Here we report the serendipitous discovery of a newly born, normal type IIb supernova (SN 2016gkg), which reveals a rapid brightening at optical wavelengths of about 40 magnitudes per day. The very frequent sampling of the observations allowed us to study in detail the outermost structure of the progenitor of the supernova and the physics of the emergence of the shock. We develop hydrodynamical models of the explosion that naturally account for the complete evolution of the supernova over distinct phases regulated by different physical processes. This result suggests that it is appropriate to decouple the treatment of the shock propagation from the unknown mechanism that triggers the explosion.