On the energy source of ultra-stripped supernovae

TL;DR

This study investigates the energy sources of ultra-stripped supernovae through long-term simulations, nucleosynthesis calculations, and light curve analysis, revealing that some are powered by radioactive nickel decay while others may involve neutron star winds.

Contribution

It provides the first detailed modeling of ultra-stripped supernovae progenitors, nucleosynthesis, and light curves, and explores alternative energy mechanisms beyond radioactive decay.

Findings

SN2019dge can be explained by $^{56}$Ni decay from a progenitor with $M_{CO} \\lesssim 1.6 M_\\odot$.

iPTF14gqr's light curve cannot be solely explained by $^{56}$Ni decay, suggesting alternative energy sources.

A magnetar with $B_p \\sim 10^{15}$ G and $P_i \\sim 0.1$ s could power iPTF14gqr.

Abstract

Ultra-stripped supernovae (USSN) with a relatively low ejecta mass of $\sim0.1M_\odot$ (e.g., iPTF14gqr and SN2019dge) are considered to originate from ultra-stripped carbon-oxygen (CO) cores in close binary systems and are likely to be progenitors of binary neutron stars (BNSs). Here we conduct long-term simulations of USSNe from ultra-stripped progenitors with various masses ($1.45\,M_\odot \leq M_\mathrm{CO} \leq 2.0\,M_\odot$) based on results of neutrino-radiation hydrodynamics simulations, and consistently calculate the nucleosynthesis and the SN light curves. We find that a USSN from a more massive progenitor has a larger ejecta mass but a smaller $^{56}$Ni mass mainly due to the fallback, which leads to the light curve being dimmer and slower. By comparing the synthetic light curves with the observed ones, we show that SN2019dge can be solely powered by $^{56}$Ni synthesized during the explosion of a progenitor with $M_\mathrm{CO} \lesssim 1.6\,M_\odot$ while iPTF14gqr cannot be explained by the $^{56}$Ni powered model; $\sim 0.05M_\odot$ of $^{56}$Ni inferred from the light curve fitting is argued to be difficult to synthesize for ultra-stripped progenitors. We consider fallback accretion onto and rotation-powered relativistic wind from the newborn NS as alternative energy sources and show that iPTF14gqr could be powered by a newborn NS with a magnetic field of $B_p \sim 10^{15}\,\mathrm{G}$ and an initial rotation period of $P_i \sim 0.1\,\mathrm{s}$.