On the Energy Sources of the Most Luminous Supernova ASASSN-15lh

TL;DR

This paper evaluates and refines energy-source models for the extremely luminous supernova ASASSN-15lh, demonstrating that models incorporating gamma-ray leakage and fallback accretion can successfully reproduce its observed light curve.

Contribution

The study introduces a revised CSI plus magnetar model with gamma-ray leakage and a new hybrid CSI plus fallback model, both capable of fitting the supernova's light curve.

Findings

Revised CSI plus magnetar model fits the light curve with gamma-ray leakage.

Hybrid CSI plus fallback model also reproduces the light curve.

Estimated fallback accreted mass is approximately 3.9 solar masses.

Abstract

In this paper, we investigate the energy-source models for the most luminous supernova ASASSN-15lh. We revisit the ejecta-circumstellar medium (CSM) interaction (CSI) model and the CSI plus magnetar spin-down with full gamma-ray/X-ray trapping which were adopted by \cite{Chatzopoulos16} and find that the two models cannot fit the bolometric LC of ASASSN-15lh. Therefore, we consider a CSI plus magnetar model with the gamma-rays/X-rays leakage effect to eliminate the late-time excess of the theoretical LC. We find that this revised model can reproduce the bolometric LC of ASASSN-15lh. Moreover, we construct a new hybrid model (i.e., the CSI plus fallback model), and find that it can also reproduce the bolometric LC of ASASSN-15lh. Assuming that the conversion efficiency ($\eta$) of fallback accretion to the outflow is typically $\sim10^{-3}$, we derive that the total mass accreted is $\sim3.9~M_\odot$. The inferred CSM mass in the two models is rather large, indicating that the progenitor could have experienced an eruption of hydrogen-poor materials followed by an energetic core-collapse explosion leaving behind a magnetar or a black hole.