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

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 $\sim 1-30$ cm${}^{-3}$. Higher resolution spectra indicate an expansion velocity around 180 km s${}^{-1}$ with a $\sim 45$ 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 ($\simeq 2700-4400$ 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.

19 pages, 6 figures, and 5 tables. Accepted for publication in ApJ

References in corpus (8)

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