Peering into the Milky Way by FAST: IV. Identification of two new Galactic supernova remnants G203.1+6.6 and G206.7+5.9

A5° × 7° sky area containing two large radio structures of G203.1+6.6 and G206.7+5.9 with a size of about 2°.5 and 3°.5 respectively is scanned by using the L-band 19-beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The FAST L-band receiver covers a frequency range of 1.0–1.5 GHz. Commissioning of the receiving system, including the measurements of the half-power beam width, gain, and main-beam efficiency is made by observing the calibrators. The multi-channel spectroscopy backend mounted to the receiver allows an in-band spectral-index determination. The brightness-temperature spectral indices of both objects are measured to be β ∼ ‑2.6 to ‑2.7. Polarized emission is detected from the archival Effelsberg λ11 cm data for all the shell structures of G203.1 +6.6 and G206.7+5.9. These results clearly indicate a non-thermal synchrotron emitting nature, confirming that G203.1+6.6 and G206.7+5.9 are large shell-type supernova remnants (SNRs). Based on morphological correlation between the radio continuum emission of G206.7+5.9 and the HI structures, the kinematic distance to this new SNR is estimated to be about 440 pc, placing it in the Local Arm.