RADIO OBSERVATIONS OF THE REMNANT OF THE SUPERNOVA OF AD-1006 .2. POLARIZATION OBSERVATIONS

We report observations in polarized flux of the remnant of the superno va of AD 1006 (SN 1006) made with the Very Large Array of the National Radio Astronomy Observatory at 1370 and 1665 MHz, at a resolution of 24''. These observations complement the total-intensity observations r eported in Paper I {Reynolds & Gilmore [AJ, 92, 1138 (1986)]}. The gro ss morphology in polarized intensity is ''bipolar,'' similar to that i n total intensity: two bright limbs across from one another. However, the SE quadrant, faintest in total intensity, shows significant polari zed flux, while the extension to the NE, fairly bright in total intens ity, appears almost unpolarized. Significant polarized flux is also se en in the remnant center, where a substantial amount of total flux is missing because of the lack of short interferometer spacings. These re solution effects make absolute determinations of the polarized fractio n uncertain, but since the polarized intensity is less smoothly distri buted than total intensity, due to rotations of polarized position ang le, little polarized flux is expected to be resolved out, and the rati o of polarized to total intensity should provide an upper limit to the polarized fraction. We find an integrated polarized fraction (measure d polarized flux divided by total flux, taken from published single-di sh observations) of about 13%; locally, however, ratios as high as 30% may occur. Our observations at two frequencies, coupled with the low, smoothly distributed rotation measure reported in previous observatio ns, can be used to infer an intrinsic polarization position angle. We deduce that the ordered component of the magnetic field is primarily r adial, as is the case in the other historical shell remnants, but our polarized-fraction upper limits imply that the magnetic field is domin antly disordered, and we estimate that the radial component contains o nly about 20% of the total magnetic energy density. Previous observati ons indicated a very low rotation measure toward SN 1006, of order 20 radians m-2, so that it is reasonable to ignore possible excess rotati ons of 2pi radians between 1370 and 1665 MHz. Making this assumption, we exhibit a low-resolution rotation-measure (RM) map; the mean RM is 16 radians m-2 in the SW lobe and 28 radians m-2 in the NE lobe, with a real dispersion (much larger than errors) of about 15 radians m-2 in each region. The bright extragalactic source in the E rim is polarize d at about the 11% level (at 24'' resolution).