2004A&A...415.1051M

We present the first CCD flux-calibrated images of the supernova remnant G 82.2+5.3 in major optical emission lines. The medium ionization line of [OIII]5007 Å provides the first direct evidence of optical emission originating from G 82.2+5.3. Filamentary emission is detected in the west and east areas of the remnant, roughly defining an ellipsoidal shell. The [OIII] emission is rather well correlated with the radio emission suggesting their association, while typical fluxes are found in the range of 20-30x10^–17erg/s/cm²/arcsec². Deep long-slit spectra taken at specific positions of the remnant verify that the detected filamentary emission originates from shock heated gas, while the diffuse [OIII] emission in the south results from photoionization processes. The spectra further suggest shock velocities around 100km/s and low electron densities. The X-ray surface brightness is quite patchy, missing obvious limb brightening and is dominated by a bright bar-like emission region which is off-set from the geometric center by ∼9'. The X-ray emission is thermal and requires two temperatures of 0.2keV and 0.63keV. The bright bar region shows overabundant Mg, Si and Fe, which might indicate still radiating ejecta matter. The azimuthally averaged radial surface profile is consistent with the matter density changing with distance r from the center ∝e^–r/r0_^ with a characteristic angular length of 36', or, alternatively, with an r^–1/2 density profile. The matter inside the remnant is quite likely structured like a porous cloudy medium. The average matter density is ∼0.04xd₁.6verb+⁺⁺±0.5^ with d_1.6 the distance in units of 1.6∼kpc. Because of the low density and the long cooling times involved the remnant is more likely to be in the adiabatic phase, which is consistent with the densities derived for the X-ray plasma and the optical line emission, but it is not excluded that is has reached the radiating phase. This, however, would imply a lower density, greater age and much larger distance, at the edge of the upper limits obtained from N_H and E(B-V).