Abstract
Context. The vast majority of Galactic supernova remnants (SNRs) were detected by their synchrotron radio emission. Recently, the evolved SNR G107.0+9.0 with a diameter of about 3° or 75 pc up to 100 pc in size was optically detected with an indication of faint associated radio emission. This SNR requires a detailed radio study. Aims. We aim to search for radio emission from SNR G107.0+9.0 by analysing new data from the Effelsberg 100-m and the Urumqi 25-m radio telescopes in addition to available radio surveys. Methods. Radio SNRs outside of the Galactic plane, where confusion is rare, must be very faint if they have not been identified so far. Guided by the Hα emission of G107.0+9.0, we separated its radio emission from the Galactic large-scale emission. Results. Radio emission from SNR G107.0+9.0 is detected between 22 MHz and 4.8 GHz with a steep non-thermal spectrum, which confirms G107.0+9.0 as an SNR. Its surface brightness is among the lowest known for Galactic SNRs. Polarised emission is clearly detected at 1.4 GHz but is fainter at 4.8 GHz. We interpret the polarised emission as being caused by a Faraday screen associated with G107.0+9.0 and its surroundings. Its ordered magnetic field along the line of sight is below 1 μG. At 4.8 GHz, we identified a depolarised filament along the western periphery of G107.0+9.0 with a magnetic field strength along the line of sight B||~ 15 μG, which requires magnetic field compression. Conclusions. G107.0+9.0 adds to the currently small number of known, evolved, large-diameter, low-surface-brightness Galactic SNRs. We have shown that such objects can be successfully extracted from radio-continuum surveys despite the dominating large-scale diffuse Galactic emission.
Highlights
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
Identified SNRs are rare, while most SNRs are identified by their non-thermal radio emission
Synchrotron emissivity towards G107.0+9.0 From the Faraday screen (FS) model result, we found that about 67% of the observed polarised emission towards G107.0+9.0 originates in its foreground, so we can estimate the synchrotron emissivity
Summary
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. 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. Identified SNRs are rare, while most SNRs are identified by their non-thermal radio emission. The radio emission of new optically detected SNRs must be unusually faint or suffer from confusion with unrelated emission in the Galactic plane. Otherwise, they would already have been identified from
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