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Blazar jets

Radial evolution of a static magnetic shear. (For details see the ApJ paper)

Blazars are a special kind of active galactic nucleus. They are thought to have a supermassive black hole at their centre, that drives a relativistic jet in a direction very close to our line of sight.

The composition of the jet is uncertain. Close to its core it may contain very little plasma and be highly relativistic. In this case, the electromagnetic fields it contains behave more like vacuum fields than the "frozen-in" fields that are familiar in ideal magnetohydrodynamics.

We have studied how these fields behave when the plasma close to the black hole is launched with a twisted magnetic field. As the plasma moves radially outwards, the density drops, and the fields try to "break free". This causes a delayed acceleration phase that can start at large distance (tens of thousands of gravitational radii) from the black hole.

We speculate that gamma-ray photons could be created in this region, and show that if this happens, they would preserve the very rapid variations imprinted on the jet by the twisted field at its base.

This could explain how some blazars (e.g.,  PKS 2155-304) emit TeV gamma-rays with an intensity that varies extremely rapidly. 


Recent contributions

I. Mochol, PhD thesis, 2012
Nonlinear waves in Poynting-flux dominated outflows

Kirk, John G. & Mochol, Iwona 2011, The Astrophysical Journal
Charge-starved, Relativistic Jets and Blazar Variability

Kirk, John G. & Mochol, Iwona 2011, IAU Symposium Waves in Poynting-flux dominated jets