G107.0+9.0: a new large optically bright, radio, and X-Ray faint galactic supernova remnant in Cepheus

Abstract

Wide-field Hα 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 Hα and [O III] 5007 Å images show dozens of Hα filaments along the remnant’s northern, western, and southwestern limbs, but few [O III] bright filaments. The nebula is well detected in the Hα 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]/Hα ratios above 0.5, consistent with shock-heated line emission. Emission line ratios suggest shock velocities ranging from ≤70 km s−1 along its western limb to ≃ 100 km s−1 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 Hα and [O III] emissions, we estimate the remnant’s distance at ∼1.5 − 2.0 kpc implying a physically large (dia. = 75 − 100 pc) and old (90 − 110 × 103 yr) SNR in its post-Sedov radiative phase of evolution expanding into a low density interstellar medium (n0 = 0.05 − 0.2 cm−3) and lying some 250 − 300 pc above the Galactic plane.

Radio properties of the optically identified supernova remnant G107.0+9.0

“…Its distance is 900 pc based on its dispersion measure. Thus, the pulsar is closer than G107.0+9.0 according to the 1.5 kpc to 2 kpc distance quoted by Fesen et al (2020). Its smaller absolute RM is in accordance with that of extragalactic sources, which trace the magnetised interstellar medium throughout the entire Galactic disk, and indicate a magnetic field direction pointing away from us throughout the Galaxy.…”

“…When searching for faint planetary nebula, Yuan & Liu (2013) noticed Hα emission from an almost spherical object with a diameter of about 3 • , which they proposed to be a so far unidentified supernova remnant (SNR). Fesen et al (2020) confirmed G107.0+9.0 as an SNR based on optical imaging in several lines and spectroscopic observations, which revealed shock velocities between 70 km s −1 and 100 km s −1 . Fesen et al (2020) estimated the distance of G107.0+9.0 between 1.5 kpc and 2 kpc, implying a size of 75 pc to 100 pc.…”

“…Fesen et al (2020) confirmed G107.0+9.0 as an SNR based on optical imaging in several lines and spectroscopic observations, which revealed shock velocities between 70 km s −1 and 100 km s −1 . Fesen et al (2020) estimated the distance of G107.0+9.0 between 1.5 kpc and 2 kpc, implying a size of 75 pc to 100 pc. The SNR is likely in the radiative phase, expanding in a low-density interstellar medium about 235 pc to 315 pc above the Galactic plane.…”

“…Diffuse large-scale Galactic emission, however, dominates at low frequencies, so objects like G107.0+9.0 with a diameter of about 3 • are either masked or cause just small intensity fluctuations. Fesen et al (2020) noticed a coincidence with faint radio-continuum emission in the medium-resolution 1420-MHz northern-sky survey by Reich (1982). This indicates that radio emission should be visible in low-frequency surveys as well, and we checked the 22-MHz survey (Roger et al 1999) and the 408-MHz survey (Haslam et al 1982).…”

“…2.1. Hα emission Fesen et al (2020) presented high-quality optical images and spectra to identify G107.0+9.0 as an SNR. Here, we used the public all-sky Hα map with 6 angular resolution or less by Finkbeiner (2003), which is a combination of various Hα surveys and includes G107.0+9.0.…”