VLA Observations of J1228+441, a Luminous Supernova Remnant in NGC 4449

Abstract

The luminous, oxygen-rich supernova remnant, J1228+441, is located in the irregular galaxy NGC 4449 and has been observed at radio wavelengths for thirty years. An analysis of recent VLA observations of NGC 4449, combined with VLA archive data and previously published VLA and WSRT observations, yields light curves at 6 and 20 cm from 1972 to 2002. The light curves at all radio frequencies exhibit a marked decline in radio emission, confirming past findings. This paper presents and discusses the radio light curves and spectral index, alpha, variations from 1972 to 2002 where nu propto nu^(-alpha) and compares J1228+441 with other radio supernovae. The spectral index of J1228+441 appears to have steepened in the last five years at higher frequencies from alpha=0.64 +- 0.02 in 1996 to alpha=1.01 +- 0.02 in 2001-2002.