THE EXPANSION OF THE RADIO REMNANT OF THE SUPERNOVA OF 1006-AD

We have reobserved the remnant of SN 1006 AD with the Very Large Array of the National Radio Astronomy Observatory1 at 1370 and 1665 MHz. We compare the resulting images with those reconstructed from observations made in 1983-1984 by Reynolds & Gilmore and find that expansion has occurred in the eight intervening years. The mean expansion in this period is 3.5 +/- 1 arcsec, implying an expansion rate of 0.049 % yr - 1 or R is-proportional-to t0.48 +/- 0.13, consistent with Sedov expansion, or with a forward/reverse shock pair moving into constant-density material. There is some evidence that the expansion rate is not uniform around the shell, being slightly smaller in the southwest quadrant. Our mean value, based on the remnant periphery as a whole, is somewhat higher than that found for an optical filament in the NW quadrant by Long et al. [ApJ, 333, 749 (1988)]; unfortunately, the radio emission is too weak in that quadrant for us to derive a radio expansion rate there. Our value is marginally consistent with a prediction of an expansion rate, R is-proportional-to t0.60, by Hamilton et al. [ApJ, 300, 698 (1986)] based on fitting the x-ray data. We discuss the significance of these observations for the dynamics of young SNRs.