RADIO OBSERVATIONS OF THE BRIGHT X-RAY SUPERNOVA REMNANT G156.2+5.7

Radio continuum emission has been observed from the bright X-ray supernova remnant RX04591 + 1547 (= G156.2 + 5.7), which has been recently detected with the ROSAT Observatory. The Effelsberg 100-m telescope has been used to map this object at 1448 MHz and 2695 MHz. Radio emission from a highly polarized non-thermal shell with a diameter of 1.9-degrees and a spectral index of alpha = 0.50 +/- 0.15 (S approximately nu(-alpha)) has been found. G156.2 + 5.7 has a surface brightness at 1 GHz of 5.8.10(-23) W m-2 Hz-1 sr-1, which is the lowest among all known supernova remnants. An area of 6-degrees x 5-degrees centered on this object has been observed in the HI line. The determination of the kinematical distance of G156.2 + 5.7 based on the HI line data turns out to be problematic. The most likely distance is between 3 kpc and 1 kpc. Thus, the diameter of the radio continuum shell is between 100 pc and 33 pc. A weak HI shell may be associated with the supernova remnant. At 3 (1) kpc distance its diameter is about 140 (47) pc and the mass is about 6300 (700) M.. This shell may have been created by the action of the stellar wind of a massive progenitor leaving a low density cavity, which is inferred by the X-ray observations.