Optical investigation of supernova remnant G206.7+5.9

ABSTRACT 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. 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 (${\rm H} \, \alpha$ and [S ii]) images with the 1-m T100 telescope. The filamentary structure seen in the ${\rm H} \, \alpha$ 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 [S ii]/${\rm H} \, \alpha$$\sim$ (0.61–1.78) and [N ii]/${\rm H} \, \alpha$$\sim$ (0.63–1.92) consistent with that expected for a shock-heated SNR. The emission lines [O i] $\lambda \lambda$6300, 6363 detected in the spectra also support the presence of shocks. Electron density ($n_{\rm e}$) measurements based on the [S ii] $\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 H i data and have newly identified an expanding gas motion of the H i, 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.