The resolved structure of the extragalactic supernova remnant SNR 4449-1
  We present very long baseline interferometry (VLBI) observations of the
milliarcsecond-scale radio structure of the supernova remnant SNR 4449$-$1 in
the galaxy NGC 4449. This young and superluminous remnant was observed at 1.6
GHz ($\lambda = 18$\,cm) with the European VLBI Network. The observations
confirm earlier identifications of this object with a supernova remnant (SNR)
while revealing a somewhat different morphology compared with the structure
reported by Bietenholz et al. from VLBI observations at 1.4 GHz. This
difference is discussed here in the context of structural sensitivity of both
observations. The 1.6 GHz image yields accurate estimates of the size (0.0422
arcsec $\times$ 0.0285 arcsec and 0.8 $\times$ 0.5 pc) and age ($\sim$55 yr) of
SNR 4449$-$1. With a total flux of 6.1 $\pm$ 0.6 mJy measured in the VLBI
image, the historical lightcurve of the source can be well represented by a
power-law decay with a power index of $-$1.19 $\pm$ 0.07. The SNR exhibits a
decline rate of the radio emission of 2.2$%$ $\pm$ 0.1$%$ yr$^{-1}$ and a radio
luminosity of 1.74 $\times$ 10$^{35}$ erg s$^{-1}$.
