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Supernova remnant (SNR) candidates in the giant spiral galaxy M101 have beenpreviously identified from ground-based H-alpha and [SII] images. We have usedarchival Hubble Space Telescope (HST) H-alpha and broad-band images as well asstellar photometry of 55 SNR candidates to examine their physical structure,interstellar environment, and underlying stellar population. We have alsoobtained high-dispersion echelle spectra to search for shocked high-velocitygas in 18 SNR candidates, and identified X-ray counterparts to SNR candidatesusing data from archival observations made by the Chandra X-ray Observatory.Twenty-one of these 55 SNR candidates studied have X-ray counterparts, althoughone of them is a known ultra-luminous X-ray source. The multi-wavelengthinformation has been used to assess the nature of each SNR candidate. We findthat within this limited sample, ~16% are likely remnants of Type Ia SNe and~45% are remnants of core-collapse SNe. In addition, about ~36% are largecandidates which we suggest are either superbubbles or OB/HII complexes.Existing radio observations are not sensitive enough to detect the non-thermalemission from these SNR candidates. Several radio sources are coincident withX-ray sources, but they are associated with either giant HII regions in M101 orbackground galaxies. The archival HST H-alpha images do not cover the entiregalaxy and thus prevents a complete study of M101. Furthermore, the lack of HST[SII] images precludes searches for small SNR candidates which could not beidentified by ground-based observations. Such high-resolution images are neededin order to obtain a complete census of SNRs in M101 for a comprehensiveinvestigation of the distribution, population, and rates of SNe in this galaxy.

Physical Structure and Nature of Supernova Remnants in M101