MAGNETIC-FIELDS IN YOUNG SUPERNOVA-REMNANTS

Magnetic field strengths in several young Type I supernova remnants (SNRs), such as those associated with SN 1572, 1604, 1006, have been previously inferred from radio synchrotron observations to be of the order of approximately 10(-4)-10(-3) G, which greatly exceeds the typical magnetic field strength of several microgauss in ambient interstellar media (ISM). Existing radio polarization studies indicate that projected large-scale magnetic fields tend to orient in the radial direction with several percent in excess within shells of these SNRs. We propose in this Letter that magnetic fields in these young SNRs could mainly originate from magnetized envelopes or magnetospheres of their presupernova progenitors, presumably magnetic white dwarfs, and that magnetic fields entrained in stellar ejecta roughly scale as approximately r-1. The inferred excess of radial alignment for magnetic fields in these young SNRs could result from the Rayleigh-Taylor instability and/or the presence of large-scale random helices of magnetic field lines with their axes meandering through the SNR shell. Molecular clouds and clumps of stellar materials surrounding the presupernova progenitor could also produce radial magnetic fields from transverse fields as the SNR expands into the ISM.