Discovery of an apparent high latitude galactic supernova remnant

Abstract

Deep Hα images of a faint emission complex 4.°0 × 5.°5 in angular extent and located far off the Galactic plane at l = 70.°0, b = -21.°5 reveal numerous thin filaments suggestive of a supernova remnant's (SNR's) shock emission. Low dispersion optical spectra covering the wavelength range 4500-7500 A° show only Balmer line emissions for one filament while three others show a Balmer dominated spectrum along with weak [N i] 5198, 5200 A°, [O i] 6300, 6364 A°, [N ii] 6583 A°, [S ii] 6716, 6731 A°, and in one case [O iii] 5007 A° line emission. Many of the brighter Hα filaments are visible in near-UV GALEX images presumably due to C iii] 1909 A° line emission. ROSAT All Sky Survey images of this region show a faint crescent-shaped X-ray emission nebula coincident with the portion of the Hα nebulosity closest to the Galactic plane. The presence of long, thin Balmer dominated emission filaments with associated UV emission and coincident X-ray emission suggests this nebula is a high latitude Galactic SNR despite a lack of known associated nonthermal radio emission. Relative line intensities of the optical lines in some filaments differ from commonly observed [S ii]/Hα ≥ 0.4 radiative shocked filaments and typical Balmer filaments in SNRs. We discuss possible causes for the unusual optical SNR spectra.