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Astron. Astrophys. 319, 655-663 (1997)


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New radio and soft X-ray observations of the supernova remnant G 18.95-1.1

E. Fürst 1, W. Reich 1 and B. Aschenbach 2

1 Max-Planck-Institut für Radioastronomie,  Auf dem Hügel 69,  D-53121 Bonn, Germany
2 Max-Planck-Institut für extraterrestrische Physik,  Postfach 1603,  D-85740 Garching, Germany

Received 8 March 1996 / Accepted 9 August 1996

Abstract

New observations of the Galactic 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 [FORMULA] of [FORMULA] and an interstellar absorption equivalent to [FORMULA]. No significant variation of [FORMULA] and [FORMULA] 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 [FORMULA]. The new 10.55 GHz observations made with the Effelsberg 100-m telescope confirm the previous radio spectral index of [FORMULA] = -0.28 ([FORMULA]) for the integrated flux densities. The integrated radio polarization at 10.55 GHz is about [FORMULA], peak values reach [FORMULA]. 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 [FORMULA] of the emission at 10.55 GHz and about [FORMULA] 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 [FORMULA], where [FORMULA] is the magnetic field component perpendicular to the line of sight. It requires a fast decrease of [FORMULA] 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 [FORMULA], indicating that G 18.95-1.1 is expanding in a previously created stellar wind bubble.

Key words: Supernova remnants – ISM: G 18.95-1.1 – X-rays: ISM – radio continuum: ISM

Send offprint requests to: E. Fürst

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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