Hubble Space Telescope Observations of an Extraordinary Flare in the M87 Jet

Abstract

HST-1, a knot along the M87 jet located 0farcs85 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 active galactic nucleus variability usually linked to blazars and originating in close proximity to 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 supermassive black hole in the core of the galaxy.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 9474, 10133, 10617.