The supernova remnants G 67.7+1.8, G 31.5-0.6 and G 49.2-0.7

Abstract

Optical CCD imaging and spectroscopic observations of three supernova remnants have been performed for the first time. Filamentary and diffuse emission is discovered from the supernova remnant G 67.7+1.8 located ∼82′ to the south of CTB 80's pulsar. The Hα and sulphur emission are almost equally strong at a level of ∼20 10-17 erg s-1 cm-2 arcsec-2 suggesting shock-heated emission. Electron densities less than 240 cm-3 are estimated, while the weak [OIII] emission suggests shock velocities in the range of 60-80 kms-1. Emission can also be seen in the ROSAT All Sky Survey data which indicate an extended hard X-ray source. Emission from G 31.5-0.6 is detected only in the Hα + [NII] image at a typical flux level of 35 10-17 erg s-1 cm-2 arcsec-2. The morphology of the observed radiation is diffuse and partially correlated with the non-thermal radio emission. Deep long-slit spectra detect sulphur line emission which is not strong enough to identify it as emission from shocked gas. Finally, optical emission from G 49.2-0.7 is obscured by several dark nebulae which probably give rise to significant X-ray attenuation. The Hα + [NII] flux is typically ∼40 10-17 erg s-1 cm-2 arcsec-2 while the [SII] flux is very weak, not allowing its identification as shock-heated. However, a small area of ∼3′ × 1′ emits strong sulphur flux relative to Hα ([SII]/Hα ∼ 0.6) This area is located in the south-east of G 49.2-0.7, close to the outer boundaries of the X-ray and radio emission. However, deep optical spectra would be required to firmly establish the nature of this emission and its association to G 49.2-0.7.