  We present a new optical imaging survey of supernova remnants in M83, using
data obtained with the Magellan I 6.5m telescope and IMACS instrument under
conditions of excellent seeing. Using the criterion of strong [S II] emission
relative to Halpha, we confirm all but three of the 71 SNR candidates listed in
our previous survey, and expand the SNR candidate list to 225 objects, more
than tripling the earlier sample. Comparing the optical survey with a new deep
X-ray survey of M83 with Chandra, we find 61 of these SNR candidates to have
X-ray counterparts. We also identify an additional list of 46 [O III] -selected
nebulae for follow-up as potential ejecta-dominated remnants, seven of which
have associated X-ray emission that makes them strong candidates. Some of the
other [O III]-bright objects could also be normal ISM-dominated supernova
remnants with shocks fast enough to doubly ionize oxygen, but with Halpha and
[S II] emission faint enough to have been missed. A few of these objects may
also be H II regions with abnormally high [O III] emission compared with the
majority of M83 H II regions, compact nebulae excited by young Wolf-Rayet
stars, or even background AGN. The supernova remnant Halpha luminosity function
in M83 is shifted a factor of ~ 4.5x higher than for M33 supernova remnants,
indicative of a higher mean ISM density in M83. We describe the search
technique used to identify the supernova remnant candidates and provide basic
information and finder charts for the objects.
