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Extragalactic Supernova Remnants

While the number of known Galactic Supernova Remnants (SNRs) is large (nearly 300 such sources are now known), significant limitations exist in studies of these sources that in turn limit our understanding ofExtragalactic.jpg SNR properties. These limitations include severe extinction along galactic lines of sight that significantly impedes X-ray and optical observations. In addition, large uncertainties in the distances to these sources may lead to correspondingly large uncertainties in other crucial SNR properties such as age, diameter and initial explosion energy. By instead observing SNRs located in nearby galaxies and analyzing their properties, some of these challenges may be addressed. For example, SNRs located in one particular galaxy are all essentially equidistant (that is, uncertainties in their distances are reduced to uncertainties in the distance to the host galaxy). Also, by choosing galaxies with face-on orientations located at high galactic latitudes, the effects of extinction (both galactic and internal to the target galaxy) may be minimized. Based on searches conducted in the X-ray, optical and radio (the three wavelength domains typically employed in searches for these sources), nearly 900 extragalactic SNRs are now known to exist. Such a large sample is suitable for a detailed study of SNR properties. Pannuti and his students analyzed X-ray and radio observations of nearby galaxies to first identify extragalactic SNRs and then to compare detection rates at different wavelength domains of extragalactic SNRs to determine the effects of the ambient interstellar medium in dictating the spectral properties of SNRs.