Deep optical CCD images of the supernova remnant G 15.1 - 1.6 were obtained and filamentary and diffuse emission has been discovered .
The images , taken in the emission lines of H \alpha + [ N ii ] , [ S ii ] and [ O iii ] , reveal filamentary and diffuse structures all around the remnant .
The radio emission at 4850 MHz in the same area is found to be well correlated with the brightest optical filaments .
The IRAS 60 \mu m emission may also be correlated with the optical emission but to a lesser extent .
The flux calibrated images suggest that the optical emission originates from shock-heated gas ( [ S ii ] /H \alpha > 0.4 ) , while there is a possible H ii region ( [ S ii ] /H \alpha \sim 0.3 ) contaminating the supernova remnant ’ s emission to the east .
Furthermore , deep long–slit spectra were taken at two bright filaments and also show that the emission originates from shock heated gas .
An [ O iii ] filamentary structure has also been detected further to the west but it lies outside the remnant ’ s boundaries and possibly is not associated to it .
The [ O iii ] flux suggests shock velocities into the interstellar `` clouds ” \sim 100 km s ^ { -1 } , while the [ S ii ] \lambda \lambda 6716 / 6731 ratio indicates electron densities up to \sim 250 cm ^ { -3 } .
Finally , the H \alpha emission has been measured to be between 2 to 7 \times 10 ^ { -16 } erg s ^ { -1 } cm ^ { -2 } arcsec ^ { -2 } , while the lower limit to the distance is estimated at 2.2 kpc .