The brightness and polarization structure of the suspected supernova remnant 3 C 58 at centimetre wavelengths

Maps of the brightness and polarization distributions over the radio source 3 C 58 have been made with the Westerbork Synthesis Radio Telescope at lambda's 6, 21 and 50 cm. The high resolution (7'' x 8'' arc at lambda 6 cm) reveals considerable fine structure in both total and polarized emission. The total intensity distribution shows no sign of shell structure. Percentage polarizations are commonly 25, 15 and 2% at lambda's 6, 21 and 50 cm, respectively. The spectrum of the integrated emission is very flat and may be represented by a power law of spectral index α = -0.09 (S proportional to νsup(α)) from 38 MHz to 15 GHz. Intercomparison of maps at different frequencies enables the following conclusions to be drawn: a) with the possible exception of the eastern and western edges, there is little variation of spectral index over 3 C 58 between lambda 50 cm and lambda 2 cm. b) The rotation measure varies rather smoothly over the source, ranging from approximately equal to -60 rad m-2 in the east to approximately equal to -125 rad m-2 in the west. c) The percentage polarization decreases steadily with increasing wavelength, probably a consequence of Faraday depolarization within the source itself. d) The component of magnetic field perpendicular to the line of sight is predominately aligned east-west, but with a pronounced outward 'bulging' in the central regions, suggestive of past or continuing activity in the centre of the source. e) The fine-scale features in the brightness distribution tend to be elongated along the magnetic field. The nature of the source is discussed and it is concluded that 3 C 58 is probably a Galactic supernova remnant, resembling the Crab Nebula in its radio properties. (orig.)