Magnetar Driven Shock Breakout and Double Peaked Supernova Light Curves

TL;DR

This paper proposes that magnetar-driven shock breakout emissions can produce observable double-peaked supernova light curves, providing a potential signature of the central engine and explaining features in recent observations.

Contribution

It introduces a model for magnetar-driven shock breakout emission and discusses conditions under which it produces a double-peaked supernova light curve, highlighting the importance of early thermal heating suppression.

Findings

Shock breakout occurs days after explosion at optical/UV wavelengths.

Double-peaked light curves may result from suppressed early magnetar heating.

Breakout signatures can be subtle, appearing as bumps or velocity changes.

Abstract

The light curves of some luminous supernovae are suspected to be powered by the spindown energy of a rapidly rotating magnetar. Here we describe a possible signature of the central engine: a burst of shock breakout emission occurring several days after the supernova explosion. The energy input from the magnetar inflates a high-pressure bubble that drives a shock through the pre-exploded supernova ejecta. If the magnetar is powerful enough, that shock will near the ejecta surface and become radiative. At the time of shock breakout, the ejecta will have expanded to a large radius (~10^{14} cm) so that the radiation released is at optical/ultraviolet wavelengths (T ~ 20,000 K) and lasts for several days. The luminosity and timescale of this magnetar driven shock breakout are similar to the first peak observed recently in the double-peaked light curve of SNLSQ14BDQ. However, for a large region of model parameter space, the breakout emission is predicted to be dimmer than the diffusive luminosity from direct magnetar heating. A distinct double peaked light curve may therefore only be conspicuous if thermal heating from the magnetar is suppressed at early times. We describe how such a delay in heating may naturally result from inefficient dissipation and thermalization of the pulsar wind magnetic energy. Without such suppression, the breakout may only be noticeable as a small bump or kink in the early luminosity or color evolution, or as a small but abrupt rise in the photospheric velocity. A similar breakout signature may accompany other central engines in supernovae, such as a black hole accreting fallback material.