1997A&A...319..655F

New observations of the Galactic supernova remnant (SNR) G 18.95-1.1 have been obtained in soft X-rays and at 10.55GHz. 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 kT_x of 0.95keV and an interstellar absorption equivalent to N_H=3.4x10²¹cm^–2. No significant variation of kT_x and N_H 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 1.48x10^–11erg/cm²/s. The new 10.55GHz observations made with the Effelsberg 100-m telescope confirm the previous radio spectral index of α=-0.28 (S_ν∝ν^α) for the integrated flux densities. The integrated radio polarization at 10.55GHz 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 large-scale centrally peaked diffuse emission, comprising about 80% of the emission at 10.55GHz 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_{{perpendicular}}(r)^1–α N_syn(r)∝n²_e(r), where B_{{perpendicular}} is the magnetic field component perpendicular to the line of sight. It requires a fast decrease of B_{{perpendicular}} 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 (1991ApJ...373..543W) 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 0.01cm^–3, indicating that G 18.95-1.1 is expanding in a previously created stellar wind bubble.