  Ultraluminous X-ray sources (ULXs) have been described variously as the most
luminous normal X-ray binaries, as hypernovae, and as "intermediate-mass" black
holes with masses of hundreds to thousands of solar masses. We present results
on M74 X-1 (CXOU J013651.1+154547), a ULX in the nearby spiral galaxy M74 (NGC
628), from observations by Chandra and XMM-Newton. M74 X-1is a persistent
source which exhibits extreme variability and changes in spectral state on
timescales of several thousand seconds. Its variability timescales and behavior
resemble some Galactic microquasars. This suggests that the emission mechanism
may be related to relativistically beamed jets, and that M74 X-1 could be an
extragalactic "microblazar" -- a microquasar whose jet axis is aligned with our
line of sight. We also note that its spectrum is consistent with the presence
of a low-temperature disk blackbody component, which, assuming it is due to
radiation from an accretion disk, could indicate that M74 X-1 contains an
intermediate-mass black hole.
