INDICATION OF THE BLACK HOLE POWERED JET IN M87 BY VSOP OBSERVATIONS

Abstract

In order to study the collimation and acceleration mechanism of relativistic jets, the jet streamline of M87 at milliarcsecond scale is extensively investigated with images from VSOP observations at 1.6 and 5 GHz. Thanks to the higher angular resolution of VSOP, especially in the direction transverse to the jet, we resolved the jet streamline into three ridgelines at the scale of milli arcseconds. While the properties of the outer two ridgelines are in good agreement with those measured in previous observations and can be expressed by one power-law line with a power law index of 1.7, an inner ridgeline is clearly observed for the first time. We compared the measured size with the outermost streamline expected by Blandford & Znajek's parabolic solutions, which are anchored at the event horizon, with different black hole spin parameters. We revealed that the observed inner ridgeline is narrower than the prediction, suggesting the origin of the inner ridgeline to be part of a spine originating from the spinning black hole. The inner ridgeline becomes very dim at large distances from the central engine at 5 GHz. We considered two possible cases for this; Doppler beaming and/or radiative cooling. Either case seems to be reasonable for its explanation, and future multi-frequency observations will discriminate those two possibilities.