Optical investigation of supernova remnant G206.7+5.9

The shell-type supernova remnant (SNR) G206.7+5.9 was recently discovered in the radio band with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The remnant spans about 3.5 in diameter and exhibits bilateral shells. In this work, we present optical spectra of G206.7+5.9 with the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST), and narrow-band (H$\alpha$ and [SII]) images with the 1-m T100 telescope. The filamentary structure seen in H$\alpha$ image shows a clear correlation with the radio emission. We use optical line ratios to determine the physical parameters of G206.7+5.9. The LAMOST spectra reveal large ratios of [SII]/H$\alpha$ $\sim$ (0.61-1.78) and [NII]/H$\alpha$ $\sim$ (0.63-1.92) consistent with that expected for a shock-heated SNR. The emission lines [OI] $\lambda$6300, $\lambda$6363 detected in the spectra also support the presence of shocks. Electron density ($n_{\rm e}$) measurements based on the [SII] $\lambda$6716/$\lambda$6731 ratio suggest densities between 117 and 597 cm$^{-3}$. We estimate the pre-shock cloud density ($n_{\rm c}$) to be approximately 2.6$-$13.3 cm$^{-3}$. We also investigate the archival HI data and have newly identified an expanding gas motion of the HI, whose velocity span is approximately 10 km s$^{-1}$. We conclude that G206.7+5.9 is an SNR exhibiting properties remarkably similar to those seen in Galactic SNRs.