The Nature of the Young Supernova Remnant S8 in the Dwarf Galaxy IC 1613

TL;DR

This study provides detailed optical imaging and spectroscopy of the young supernova remnant S8 in IC 1613, revealing its complex shock structures, composition, and physical properties, and comparing it to similar remnants in the LMC.

Contribution

It offers the first comprehensive optical analysis of S8, characterizing its shock velocities, densities, and age, and establishing its similarities to the LMC remnant N49.

Findings

S8 is approximately 2700-4400 years old.

The remnant exhibits a wide range of shock velocities from 50 to over 350 km/s.

The nebula's mass is estimated at 119 ± 34 solar masses.

Abstract

We present sub-arcsecond optical images and low- to moderate-resolution spectra of the compact, X-ray and optically bright supernova remnant known as S8 in the nearby dwarf galaxy IC 1613. Deep H$\alpha$ images of the remnant show a sharply defined crescent shaped nebula, while narrow passband images reveal a coincident and unexpectedly bright continuum nebulosity exhibiting a size and morphology like that seen for the remnant's line emissions. Low-dispersion spectra covering 3600 - 9000 A show numerous low-ionization line emissions such as [O I] and [Fe II], along with higher-ionization emission lines including He II and optical coronal lines [Fe VII], [Fe X], [Fe XI], and [Fe XIV]. This suggests the presence of a wide range of shock velocities from $\sim$ 50 to over 350 km s$^{-1}$, corresponding to preshock densities of $\sim1 - 30$ cm$^{-3}$. Higher resolution spectra indicate an expansion velocity around 180 km s$^{-1}$ with a $\sim45$ km s$^{-1}$ wide central cavity. H$\alpha$ emission spans rest frame velocities of $+120$ to $-240$ km s$^{-1}$ and we estimate a total nebula mass of $119 \pm 34$ M$_{\odot}$. We conclude S8 is a relatively young supernova remnant ($\simeq2700 - 4400$ yr) exhibiting properties remarkably like those seen in the young LMC remnant N49, including age, physical size, shock velocities, filament densities, optical line strengths, X-ray and optical luminosities, and coronal line and continuum emissions.