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Optical observations explore the nature of supernova remnant G206.7+5.9

Astronomers from Turkey and Japan have performed optical observations of a recently discovered nearby supernova remnant known as G206.7+5.9. Results of their observations, Jan. 28 on the arXiv pre-print server, provide more insights into the nature of this remnant.

Supernova remnants (SNRs) are diffuse, expanding structures resulting from a supernova explosion. They contain ejected material expanding from the explosion and other interstellar material that has been swept up by the passage of the shockwave from the exploded star.

G206.7+5.9 is a shell-type Galactic SNR discovered in 2022 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). It has a physical size of about 88 light years and is located some 1,400 light years away, within the Milky Way's Local Arm.

Previous radio observations of G206.7+5.9 have found that it contains one shell on the eastern side and two shells on the western side. However, given that G206.7+5.9 has not been studied in other wavelengths other than radio, a team of astronomers led by Hicran Bakis of the Akdeniz University in Antalya, Turkey, decided to investigate this SNR in the optical band.

For this purpose, they employed the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) and the TÃœBÄ°TAK National Observatory (TUG).

Using LAMOST, the researchers obtained optical spectra at 10 locations near the southwestern and northwestern regions of G206.7+5.9. They also obtained hydrogen-alpha and ionized sulfur [S II] spectral line images of the southwest region with TUG's 1-m T100 telescope.

The observations found that the emission from the southwestern region shows filamentary structure, in correlation with the radio emission. The LAMOST spectra revealed that the investigated regions of G206.7+5.9 showcase large ionized sulfur and ionized nitrogen to hydrogen-alpha ratios. This suggests that the emission primarily originates from shock-heated gas.

Moreover, the study detected emission lines of atomic oxygen in the spectra of G206.7+5.9. This finding further supports the presence of shock activity.

The observations also allowed the team to measure electron densities for the inspected regions of G206.7+5.9, which were found to be between 117 and 597 cm^−3, with an average ratio of around 327 cm^−3. The pre-shock cloud electron density was estimated to be approximately 2.6−13.3 cm^−3.

According to the authors of the paper, the range of pre-shock cloud densities suggests that G206.7+5.9 is interacting with a high-density clumpy interstellar medium. They estimate that the age of this SNR is between 6,000 and 14,000 years.

Summing up the results, the researchers note that G206.7+5.9 showcases characteristics strikingly similar to those observed in some other shock-heated Galactic SNRs, like G156.2+5.7.