Episodic ejection of relativistic jets by the X-ray transient GRO J1655 - 40

GRO J1655-40, a recently discovered black-hole candidate, is an ideal system for studying jets of material from the accretion disk around a black hole. Observations of the radio emission show two highly collimated relativistic jets, one on each side of the source, which expand and decay over a few days. The jet ejection, at 92% of the speed of light, appears episodic and asymmetric; the alternate brightening and fading of the jets cannot be explained by relativistic beaming.