Abstract
We present a polarimetric study of the pulsar wind nebula (PWN) in supernova remnant G21.5−0.9 using archival Very Large Array (VLA) data. The rotation measure (RM) map of the PWN shows a symmetric pattern that aligns with the presumed pulsar spin axis direction, implying a significant contribution of RM from the nebula. We suggest that the spatial variation of the internal RM is mostly caused by non-uniform distribution of electrons originating from the supernova ejecta. Our high-resolution radio polarization map reveals an overall radial B-field. We construct a simple model with an overall radial B-field and turbulence in small scale. The model can reproduce many of the observed features of the PWN, including the polarization pattern and polarized fraction. The results also reject a large-scale toroidal B-field which implies that the toroidal field observed in the inner PWN cannot propagate to the entire nebula.
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