Centrifugal acceleration of astroparticles to relativistic energies might take place in rotating astrophysical objects (see also Fermi acceleration). It is strongly believed that AGN and Pulsars have rotating magnetospheres, therefore, they potentially can drive charged particles to high and ultra high energies.
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Acceleration to high energies
It is well known that the magnetospheres of AGN and Pulsars are characterized by strong magnetic fields, which in turn, might force the charged particles to follow the field lines. On the other hand, if the magnetic field lines are rotating (which is the case for the above-mentioned astrophysical objects) the particles will inevitably undergo centrifugal acceleration. In the pioneering work by Machabeli & Rogava was considered a gedanken experiment: a bead moving inside a straight rotating pipe. Dynamics of a particle was analyzed as analytically as numerically and it has been shown that if the rigid rotation is maintained for a sufficiently long time energy of the bead will asymptotically increase. In particular, Rieger & Mannheim, based on the theory developed by Machabeli & Rogava have shown that the Lorentz factor of the bead behaves as
where
As is seen from (1), the Lorentz factor of the particle tends to infinity if the rigid rotation is maintained. This means that in reality the energy has to be limited by certain processes. Generally speaking, there are two major mechanisms: The inverse Compton scattering (ICS) and the so-called breakdown of the bead on the wire (BBW) mechanism. Considering jet-like structures in AGN it has been shown that for a wide range of inclination angles of field lines with respect to the rotation axis, the ICS is the dominant mechanism efficiently limiting the maximum attainable Lorentz factors of electrons
The centrifugal effects are more efficient in millisecond Pulsars, since the rotation rate is quite high. Osmanov & Rieger considered the centrifugal acceleration of charged particles in the light cylinder area of the Crab-like Pulsars. It has been shown that electrons might achieve the Lorentz factors
Acceleration to very high and ultra high energies
Although the direct centrifugal acceleration has limitations, as analysis shows the effects of rotation still might play an important role in the processes of acceleration of charged particles. Generally speaking, it is believed that the centrifugal relativistic effects may induce plasma waves, which under certain conditions might be unstable efficiently pumping energy from the background flow. On the second stage energy of wave-modes can be transformed into energy of plasma particles, leading to consequent acceleration.
In rotating magnetospheres the centrifugal force acts differently in different locations, leading to generation of Langmuir waves, or Plasma oscillations via the parametric instability. One can show that this mechanism efficiently works in the magnetospheres of AGN and Pulsars.
Considering Crab-like Pulsars it has been shown that by means of the Landau damping the centrifugally induced electrostatic waves efficiently lose energy transferring it to electrons. It is found that energy gain by electrons is given by
where
By examining the magnetospheres of AGN, the acceleration of protons takes place through the Langmuir collapse. As it is shown this mechanism is strong enough to guarantee efficient acceleration of particles to ultra high energies via the Langmuir damping
where