New continuum and polarization observations of the Cygnus Loop with FAST
  We report on the continuum and polarization observations of the Cygnus Loop
supernova remnant (SNR) conducted by the Five-hundred-meter Aperture Spherical
radio Telescope (FAST). FAST observations provide high angular resolution and
high sensitivity images of the SNR, which will help to disentangle its nature.
We obtained Stokes I, Q and U maps over the frequency range of 1.03 - 1.46 GHz
split into channels of 7.63 kHz. The original angular resolution is in the
range of ~3 arcmin - ~3.8 arcmin, and we combined all the data at a common
resolution of 4 arcmin. The temperature scale of the total intensity and the
spectral index from the in-band temperature-temperature plot are consistent
with previous observations, which validates the data calibration and map-making
procedures. The rms sensitivity for the band-averaged total-intensity map is
about 20 mK in brightness temperature, which is at the level of confusion
limit. For the first time, we apply rotation measure (RM) synthesis to the
Cygnus Loop to obtain the polarization intensity and RM maps. The rms
sensitivity for polarization is about 5 mK, far below the total-intensity
confusion limit. We also obtained RMs of eight extra-galactic sources, and
demonstrate that the wide-band frequency coverage helps to overcome the
ambiguity of RM determinations.
