Hydrogen-poor superluminous stellar explosions

TL;DR

This paper introduces a new class of hydrogen-poor, superluminous supernovae that are much brighter and have different properties than known types, expanding our understanding of stellar explosions and their use in studying distant galaxies.

Contribution

The discovery and characterization of a new class of hydrogen-free, superluminous supernovae with unique observational properties not explained by existing models.

Findings

These supernovae are ~10 times brighter than SNe Ia.

They emit significant UV flux over extended periods.

Their decay rates are inconsistent with radioactive decay.

Abstract

Supernovae (SNe) are stellar explosions driven by gravitational or thermonuclear energy, observed as electromagnetic radiation emitted over weeks or more. In all known SNe, this radiation comes from internal energy deposited in the outflowing ejecta by either radioactive decay of freshly-synthesized elements (typically 56Ni), stored heat deposited by the explosion shock in the envelope of a supergiant star, or interaction between the SN debris and slowly-moving, hydrogen-rich circumstellar material. Here we report on a new class of luminous SNe whose observed properties cannot be explained by any of these known processes. These include four new SNe we have discovered, and two previously unexplained events (SN 2005ap; SCP 06F6) that we can now identify as members. These SNe are all ~10 times brighter than SNe Ia, do not show any trace of hydrogen, emit significant ultra-violet (UV) flux for extended periods of time, and have late-time decay rates which are inconsistent with radioactivity. Our data require that the observed radiation is emitted by hydrogen-free material distributed over a large radius (~10^15 cm) and expanding at high velocities (>10^4 km s^-1). These long-lived, UV-luminous events can be observed out to redshifts z>4 and offer an excellent opportunity to study star formation in, and the interstellar medium of, primitive distant galaxies.