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

¹ University of Crete, Physics Department, PO Box 2208, 710 03 Heraklion, Crete, Greece
² Foundation for Research and Technology-Hellas, PO Box 1527, 711 10 Heraklion, Crete, Greece
³ Max-Planck Institut für extraterrestrische Physik, Giessenbachstrasse, 85740 Garching, Germany

Corresponding author: F. Mavromatakis, fotis@physics.uoc.gr

Received: 20 November 2000
Accepted: 12 January 2001

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 sulfur 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 km s^-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 HNii ] 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 sulfur 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 HNii ] 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 sulfur 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.