New continuum and polarization observations of the Cygnus Loop with FAST II. Images and analyses

TL;DR

This paper presents high-resolution radio images of the Cygnus Loop supernova remnant from FAST, revealing differences in magnetic fields and environmental conditions between its northern and southern parts, and analyzing their structures and properties.

Contribution

It provides detailed polarization and intensity images of the Cygnus Loop, offering new insights into its magnetic field structure and environmental differences using FAST observations.

Findings

Northern part has larger random magnetic field component.

Both parts have similar spectral indices in shell structures.

Northern and southern regions are in different interstellar environments.

Abstract

We present total-intensity and polarized-intensity images of the Cygnus Loop supernova remnant (SNR) observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The high angular-resolution and high-sensitivity images enable us to thoroughly compare the properties of the northern part with the southern part of the SNR. The central filament in the northern part and the southern part have a similar foreground rotation measure, meaning their distances are likely similar. The polarization analysis indicates that the random magnetic field is larger than the regular field in the northern part, but negligible in the southern part. The total-intensity image is decomposed into components of various angular scales, and the brightness-temperature spectral index of the shell structures in the northern part is similar to that in the southern part in the component images. All these evidence suggest that the northern and southern part of the Cygnus Loop are situated and thus evolved in different environments of interstellar medium, while belonging to the same SNR.