Particle acceleration in rotating and shearing jets from AGN

Abstract

Abstract.We model the acceleration of energetic particles due to shear and centrifugal effects in rotating astrophysical jets. The appropriate equation describing the diffusive transport of energetic particles in a collisionless, rotating background flow is derived and analytical steady state solutions are discussed. In particular, by considering velocity profiles from rigid, over flat to Keplerian rotation, the effects of centrifugal and shear acceleration of particles scattered by magnetic inhomogeneities are distinguished. In the case where shear acceleration dominates, it is confirmed that power law particle momentum solutions f (p) ∝ p −(3+α) exist, if the mean scattering time τ c ∝ p α is an increasing function of momentum. We show that for a more complex interplay between shear and centrifugal acceleration, the recovered power law momentum spectra might be significantly steeper but flatten with increasing azimuthal velocity due to the increasing centrifugal effects. The possible relevance of shear and centrifugal acceleration for the observed extended emission in AGN is demonstrated for the case of the jet in the quasar 3C273.

X‐Ray Emission Properties of Large‐Scale Jets, Hot Spots, and Lobes in Active Galactic Nuclei

“…This, in turn, would be consistent with deviation from the minimum-power condition within the considered jets themselves. We note that viscous acceleration of cosmic rays taking place at the turbulent boundary layers of relativistic jets, discussed by, e.g., Ostrowski (2000) and Rieger & Mannheim (2002), could provide an energetically important flat-spectrum population of ultrarelativistic protons within the lobes of powerful radio sources.…”

Particle Acceleration in Astrophysical Shear Flows

“…Moreover, there is also evidence for helical bulk motion in the large-scale jet (e.g., Bahcall et al 1995) and internal jet helicity (e.g., oscillating ridge line, double helical pattern, periodicity) on the VLBI mas-scale and below (e.g., Krichbaum et al 2000, Camenzind & Krockenberger 1992, suggesting that particle acceleration due to internal jet rotation (cf. Rieger & Mannheim 2002) may contribute on pc-scale and perhaps even on larger scales.…”

“…Particle acceleration in non-gradual relativistic shear flow has been considered by Ostrowski (1990Ostrowski ( , 1998Ostrowski ( , 2000; cf also Stawarz & Ostrowski 2002) based on Monte Carlo simulations, showing that very flat particle momentum spectra may be possible. More recently, Rieger & Mannheim (2002) have studied the acceleration of particles in rotating and shearing flows with application to relativistic AGN jets. Based on the insights gained from these works, shear acceleration in astrophysical jets appears in some respects unavoidable.…”

The Linear Accelerating Superluminal Motion Model

“…The maximum difference of position angles can reach 40Њ. The difference of position angles as well as viewing angles may indicate that there probably exists a supermassive binary black hole system (Sundelius et al 1997) where the orbital motion of the relativistic jet emerging from one massive black hole causes the variation of viewing angles (Rieger & Mannheim 2000). Another possible explanation is precession (Gower et al 1982), and the precession angle and period can be used to estimate the masses of the black holes (Romero et al 2000).…”

“…There is increasing evidence that the central engine of acceleration in active galactic nuclei (AGNs) is a rotating supermassive black hole surrounded by a geometrically thin accretion disk, which gives rise to the formation of a pair of relativistic jets. The mechanism of acceleration may be due to the centrifugal and shear effects (Webb et al 1994;Rieger & Mannheim 2002). In recent years, multiepoch VLBI monitoring indeed led to the discovery of parsec-scale accelerating superluminal motion in the quasar 3C 273 (Krichbaum et al 2001) and in other sources (Homan et al 2001).…”