  We study 203 (of 442) Swift AGN and Cluster Survey extended X-ray sources
located in the SDSS DR8 footprint to search for galaxy over-densities in three
dimensional space using SDSS galaxy photometric redshifts and positions near
the Swift cluster candidates. We find 104 Swift clusters with a >3sigma galaxy
over-density. The remaining targets are potentially located at higher redshifts
and require deeper optical follow-up observations for confirmation as galaxy
clusters. We present a series of cluster properties including the redshift, BCG
magnitude, BCG-to-X-ray center offset, optical richness, and X-ray luminosity.
We also detect red sequences in ~85% of the 104 confirmed clusters. The X-ray
luminosity and optical richness for the SDSS confirmed Swift clusters are
correlated and follow previously established relations. The distribution of the
separations between the X-ray centroids and the most likely BCG is also
consistent with expectation. We compare the observed redshift distribution of
the sample with a theoretical model, and find that our sample is complete for z
<~ 0.3 and is still 80% complete up to z ~= 0.4, consistent with the SDSS
survey depth. These analysis results suggest that our Swift cluster selection
algorithm has yielded a statistically well-defined cluster sample for further
studying cluster evolution and cosmology. We also match our SDSS confirmed
Swift clusters to existing cluster catalogs, and find 42, 23 and 1 matches in
optical, X-ray and SZ catalogs, respectively, so the majority of these clusters
are new detections.
