New radio and soft X - ray observations of the supernova remnant G 18 . 95 - 1 . 1

New observations of theGalactic supernova remnant (SNR) G 18.95-1.1 have been obtained in soft X-rays and at 10.55 GHz. The X-ray emission was observed with the ROSAT satellite using its position proportional counter (PSPC). The data are best fitted by a single-component, thermal spectrum with a temperature k Tx of 0.95 keV and an interstellar absorption equivalent to NH = 3.4 1021 cm−2. No significant variation of k Tx andNH across the source was detected. The upper limit of any power law emission is about 1% of the total observed X-ray flux density of 1.48 10−11 erg cm−2 s−1. The new 10.55 GHz observations made with the Effelsberg 100-m telescope confirm the previous radio spectral index of α = -0.28 (Sν ∝ ν) for the integrated flux densities. The integrated radio polarization at 10.55 GHz is about 6%, peak values reach 30%. The magnetic field direction is aligned to the arc structures. Two components contribute to the radio as well as to the X-ray emission: A largescale centrally peaked diffuse emission, comprising about 80% of the emission at 10.55 GHz and about 50% at X-rays, and small scale structures. The radial dependence of the column emissivity of the diffuse emission is very similar at radio waves and in the X-ray domain suggesting that B⊥(r)1−α Nsyn(r) ∝ ne(r), whereB⊥ is the magnetic field component perpendicular to the line of sight. It requires a fast decrease ofB⊥ towards the boundary of the source and the formation of a circumferential magnetic field. The radial dependence of the X-ray emission is in good agreement with models of White & Long (1991) for a SNR evolution in a cloudy interstellar medium, if the cloud evaporation time is very large compared with the age of the SNR. The models lead to a rather low ambient density of a few 0.01 cm−3, indicating that G 18.95-1.1 is expanding in a previously created stellar wind bubble.