2020ApJ...902...19F

We present subarcsecond 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 Hα 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 Å 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 ∼50 to over 350 km s^–1, corresponding to preshock densities of ∼1-30 cm^–3. Higher-resolution spectra indicate an expansion velocity around 180 km s^–1 with an ∼45 km s^–1 wide central cavity. The Hα emission spans rest-frame velocities of +120 to -240 km s^–1, and we estimate a total nebula mass of 119 ± 34 M_☉. We conclude that S8 is a relatively young supernova remnant (≃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.