G107.0+9.0: A New Large Optically Bright, Radio and X-Ray Faint Galactic Supernova Remnant in Cepheus

Wide-field H-alpha images of the Galactic plane have revealed a new supernova remnant (SNR) nearly three degrees in diameter centred at l = 107.0, b = +9.0. Deep and higher resolution H-alpha and [O III] 5007 Ang images show dozens of H-alpha filaments along the remnant's northern, western, and southwestern limbs, but few [O III] bright filaments. The nebula is well detected in the H-alpha Virginia Tech Spectral-Line Survey images, with many of its brighter filaments even visible on Digital Sky Survey images. Low-dispersion spectra of several filaments show either Balmer dominated, non-radiative filaments or the more common SNR radiative filaments with [S II]/H-alpha ratios above 0.5, consistent with shock-heated line emission. Emission line ratios suggest shock velocities ranging from