Hubble Space Telescope observations of an extraordinary flare in the M87
  jet
  HST-1, a knot along the M87 jet located 0.85 arcsec from the nucleus of the
galaxy has experienced dramatic and unexpected flaring activity since early
2000. We present analysis of Hubble Space Telescope Near-Ultraviolet (NUV)
imaging of the M87 jet from 1999 May to 2006 December that reveals that the NUV
intensity of HST-1 has increased 90 times over its quiescent level and
outshines the core of the galaxy. The NUV light curve that we derive is
synchronous with the light curves derived in other wavebands. The correlation
of X-ray and NUV light curves during the HST-1 flare confirms the synchrotron
origin of the X-ray emission in the M87 jet. The outburst observed in HST-1 is
at odds with the common definition of AGN variability usually linked to blazars
and originating in close proximity of the central black hole. In fact, the M87
jet is not aligned with our line of sight and HST-1 is located at one million
Schwarzchild radii from the super-massive black hole in the core of the galaxy.
