Long Plateau Doth So: How Internal Heating Sources Affect Hydrogen-rich Supernova Light Curves

Abstract

Some hydrogen-rich core-collapse supernovae (SNeIIP) exhibit evidence of a sustained energy source powering their light curves, resulting in a brighter and/or longer-lasting hydrogen recombination plateau phase. We present a semi-analytic SNIIP light-curve model that accounts for the effects of an arbitrary internal heating source, considering as special cases ⁵⁶Ni/⁵⁶Co decay, a central engine (magnetar or accreting compact object), and shock interaction with a dense circumstellar disk. While a sustained internal power source can boost the plateau luminosity commensurate with the magnitude of the power, the duration of the recombination plateau can typically be increased by at most a factor of ∼2–3 compared to the zero-heating case. For a given ejecta mass and initial kinetic energy, the longest plateau duration is achieved for a constant heating rate at the highest magnitude that does not appreciably accelerate the ejecta. This finding has implications for the minimum ejecta mass required to explain particularly long-lasting SNe, such as iPTF14hls, and for confidently identifying rare explosions of the most massive hydrogen-rich (e.g., Population III) stars. We present a number of analytic estimates that elucidate the key features of the detailed model.