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

TL;DR

This paper reports the discovery and analysis of a large, optically bright, radio and X-ray faint supernova remnant in Cepheus, characterized by filamentary structures, shock velocities, and an estimated age of 90-110 thousand years.

Contribution

It presents the identification and detailed multi-wavelength analysis of a new supernova remnant with unique optical features and faint radio/X-ray emissions, expanding knowledge of SNR diversity.

Findings

Large (~75-100 pc) SNR in Cepheus identified.

Shock velocities estimated between <70 km/s and ~100 km/s.

Remnant is old (90-110 kyr) and expanding into low-density medium.

Abstract

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 <70 km/s along its western limb to ~100 km/s along its northwestern boundary. While no associated X-ray emission is seen in ROSAT images, faint 1420 MHz radio emission appears coincident with its western and northern limbs. Based on an analysis of the remnant's spatially resolved H-alpha and [O III] emissions, we estimate the remnant's distance around 1.5 - 2.0 kpc implying a physically large (dia.= 75 - 100 pc) and old (90 - 110 x 10^3 yr) SNR in its post-Sedov radiative phase of evolution expanding into a low density interstellar medium (n = 0.05 - 0.2 cm^-3) and lying some 250 - 300 pc above the Galactic plane.