The X-ray brightest clusters of galaxies from the Massive Cluster Survey
  We present a statistically complete sample of very X-ray luminous galaxy
clusters detected in the MAssive Cluster Survey (MACS). This second MACS
release comprises all 34 MACS clusters with nominal X-ray fluxes in excess of
2x10^(-12) erg/s/cm^2 (0.1-2.4 keV) in the ROSAT Bright Source Catalogue; two
thirds of them are new discoveries. Extending over the redshift range from 0.3
to 0.5, this subset complements the complete sample of the 12 most distant MACS
clusters (z>0.5) published in 2007 and further exemplifies the efficacy of
X-ray selection for the compilation of samples of intrinsically massive galaxy
clusters. Extensive follow-up observations with Chandra/ACIS led to three
additional MACS cluster candidates being eliminated as (predominantly) X-ray
point sources. For another four clusters --- which, however, remain in our
sample of 34 --- the point-source contamination was found to be about 50%. The
median X-ray luminosity of 1.3x10^45 erg/s (0.1-2.4 keV, Chandra, within r_500)
of the clusters in this subsample demonstrates the power of the MACS survey
strategy to find the most extreme and rarest clusters out to significant
redshift. A comparison of the optical and X-ray data for all clusters in this
release finds a wide range of morphologies with no obvious bias in favour of
either relaxed or merging systems.
