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Nature. 2015 May 28;521(7553):495-7. doi: 10.1038/nature14481.

A kiloparsec-scale internal shock collision in the jet of a nearby radio galaxy.

Author information

1
1] Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA [2] University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA.
2
1] University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA [2] NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, Maryland 20771, USA.
3
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA.
4
Florida Institute of Technology, 150 West University Boulevard, Melbourne, Florida 32901, USA.
5
Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
6
1] Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA [2] Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
7
1] Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA [2] Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA [3] Istituto Nazionale Astrofisica, Istituto di Radio Astronomia, Via Piero Gobetti 101, I-40129 Bologna, Italy.

Abstract

Jets of highly energized plasma with relativistic velocities are associated with black holes ranging in mass from a few times that of the Sun to the billion-solar-mass black holes at the centres of galaxies. A popular but unconfirmed hypothesis to explain how the plasma is energized is the 'internal shock model', in which the relativistic flow is unsteady. Faster components in the jet catch up to and collide with slower ones, leading to internal shocks that accelerate particles and generate magnetic fields. This mechanism can explain the variable, high-energy emission from a diverse set of objects, with the best indirect evidence being the unseen fast relativistic flow inferred to energize slower components in X-ray binary jets. Mapping of the kinematic profiles in resolved jets has revealed precessing and helical patterns in X-ray binaries, apparent superluminal motions, and the ejection of knots (bright components) from standing shocks in the jets of active galaxies. Observations revealing the structure and evolution of an internal shock in action have, however, remained elusive, hindering measurement of the physical parameters and ultimate efficiency of the mechanism. Here we report observations of a collision between two knots in the jet of nearby radio galaxy 3C 264. A bright knot with an apparent speed of (7.0 ± 0.8)c, where c is the speed of light in a vacuum, is in the incipient stages of a collision with a slower-moving knot of speed (1.8 ± 0.5)c just downstream, resulting in brightening of both knots--as seen in the most recent epoch of imaging.

PMID:
26017450
DOI:
10.1038/nature14481

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