Abstract
Our understanding of the physics of kpc-scale quasar jets had seemed to converge to a paradigm in which these jets are as highly relativistic on the kpc scale as they are on sub-pc scales close to the central black hole. Retaining bulk Lorentz factors (Γ) on the order of 10–20 at these distances implies a jet power comparable to or higher than their Eddington luminosity. We recently started challenging this paradigm, which was put in place to explain the surprisingly bright X-ray emission of the knots of many quasar jets as inverse Compton scattering off the cosmic microwave background (IC/CMB). We have shown that the knot X-ray emission of the archetypical jets 3C 273 and PKS 0637-752 is not due to IC/CMB. With IC/CMB disfavored, an alternative interpretation for the X-rays is synchrotron radiation from a second population of electrons accelerated in situ up to ∼100 TeV. These results are the first step towards resolving the long-standing issue of the nature of the X-ray emission in powerful quasar jets. Comprehensive observational and theoretical work on essentially all X-ray-detected large-scale quasar jets to test the IC/CMB model over a much larger population needs to be done to examine the implications of slower jets that are extremely efficient accelerators. A fascinating case can be made that—contrary to popular belief—the total radiative power of the large-scale jet of these sources is comparable to that of the quasar core. Even more so, the angle-integrated TeV output of these (previously thought TeV-quiet) quasar jets likely makes them the dominant class among active galactic nuclei (AGN), exceeding the TeV production of so-called TeV blazars.
Highlights
In active galactic nuclei (AGN), relativistic jets transport energy and mass from the sub-parsec central regions to Mpc-scale lobes, with a kinetic power comparable to that of the host galaxy and the AGN, profoundly influencing the evolution of the host, nearby galaxies, and the surrounding interstellar and intracluster medium [1,2]
When combined with the broadband spectral shape of these regions, this is very difficult to explain via IC/CMB models, unless the scattering particles are at the lowest-energy tip of the electron energy distribution, with Lorentz factor γ ∼ 1, and the jet is very highly beamed (Doppler factor δ ≥ 20) and viewed within a few degrees of the line of sight (Figure 2)
The energetic demands of such a jet are extreme: if we require one proton per radiating lepton, the jet power must be at least 10× the Eddington luminosity of the black hole in PKS 1136-135, and such a configuration might result in Faraday depolarization in the radio [29]
Summary
In active galactic nuclei (AGN), relativistic jets transport energy and mass from the sub-parsec central regions to Mpc-scale lobes, with a kinetic power comparable to that of the host galaxy and the AGN, profoundly influencing the evolution of the host, nearby galaxies, and the surrounding interstellar and intracluster medium [1,2]. The generation of these flows is tied to the process of accretion onto rotating black holes, where the magneto-rotational instability can couple the black hole’s spin and magnetic field to produce high-latitude outflows close to the speed of light [3]. More powerful FR II (quasar) jets have very different spectral energy distributions
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