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A VLA Study of the Expansion of Tycho's Supernova
Remnant

Reynoso, E. M.; Moffett, D. A.; Goss, W. M.; Dubner, G. M.;
Dickel, J. R.; Reynolds, S. P.; Giacani, E. B.
*Published in:*
ApJ, 491, 816

### Abstract

We have measured the expansion of Tycho's supernova remnant (SNR) over a 10 yr
interval by comparing
new VLA observations at 1375 MHz made in 1994 and 1995 with previous
observations made in 1983 and
1984 using the same array configurations, bandwidths, calibrators, and
integration times. To compute the
expansion of the outer rim, we estimate the expansion rate for radial sectors of
4 deg. The overall mean
expansion obtained is 3."05 but varies between 1" and 5" around the shell. The
weighted average fractional
expansion rate is 0.1126% yr-1, corresponding to a power-law index (expansion
parameter) nu = d ln R/d
ln t = 0.471, with an error of ~6%. We also compute the expansion of interior
features, and find a
comparable global expansion parameter. The value of nu obtained is in excess of
the pure Sedov value of
0.4, indicating that Tycho's SNR is still in transition from an earlier phase to
the Sedov adiabatic phase of
evolution, and supporting expansion into a medium without a strong radial
density gradient, as expected for
a Type Ia supernova. In addition, the significant local variations that we
observe suggest that a unique
average expansion rate is an oversimplified description for Tycho. Both radio
flux and polarization were
found to remain almost constant during the intervening 10 years.