OPTICAL DISCOVERY OF AN APPARENT GALACTIC SUPERNOVA REMNANT G159.6+7.3

Deep H alpha images of portions of a faint 3 degrees x 4 degrees H alpha shell centered at l = 159 degrees.6, b = 7 degrees.3 seen on the Virginia Tech Spectral Line Survey images revealed the presence of several thin emission filaments along its eastern limb. Low-dispersion optical spectra of two of these filaments covering the wavelength range of 4500-7500 angstrom show narrow H alpha line emissions with velocities around -170 +/- 30 km s(-1). Both the morphology and spectra of these filaments are consistent with a Balmer-dominated shock interpretation and we propose that these optical filaments indicate that the large H alpha emission shell is a previously unrecognized supernova remnant (SNR). ROSAT All Sky Survey images indicate the possible presence of extremely faint, diffuse emission from the shell's central region. The shell's location more than 7 degrees off the Galactic plane in a region of relatively low interstellar density may account for the lack of any reported associated non-thermal radio emissions. The rare discovery of a Galactic SNR at optical wavelengths suggests that additional high-latitude SNRs may have escaped radio and X-ray detection.