Extragalactic multi-frequency searches for supernova remnants

![CDATA[This is an exciting time for the discovery of supernova remnants (SNRs) in galaxies other than our Milky Way. Here, we review recent multi-frequency searches for SNRs in the Magellanic Clouds, NGC 300 and NGC 7793. For example, high resolution (40”) and sensitive (< 0.3 mJy beam-1) Australia Telescope Compact Array (ATCA) 1.377 GHz radio images of the Large Magellanic Cloud (LMC) contain thousands of sources; 76 of these are extended and meet criteria as SNRs or SNR candidates. Similarly, ATCA mosaic images of the Small Magellanic Cloud (SMC) at 1.42 and 2.37 GHz with snapshots at 4.80 and 8.64 GHz verify the presence of 16 SNRs and 5 SNR candidates. These radio images have resolutions ranging from 98” to 15” and sensitivities from 1.8 to 0.4 mJy beam-1, respectively. 1.42 and 2.37 GHz images were co-added with Parkes single-dish data to give enhanced large scale structure (up to 4°) revealing yet more detail of each source. Radio-Hα subtraction images and 2.3-meter Dual Beam Spectrograph (DBS) observations of selected SMC regions, including N66, have resulted in the discovery of one additional SNR candidate. Radio ATCA observations at 13 and 20 cm along with XMM observations of NGC 300 have identified 18 SNRs and 3 SNR candidates within that galaxy. We also report the presence of a suspected superbubble within NGC 7793 (S-26) composed of many SNRs. For that study, we use both Chandra and 2.3-meter DBS observations.]]