Recent Progress in Understanding the Large Scale Jets of Powerful Quasars

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.

Radio Galaxies at VHE Energies

“…Evidence for a possible VHE extension has in fact been recently reported for Cen A [131]. We note that an experimental verification of extended VHE emission would support the notion that the large-scale jets in AGN could make a relevant contribution to the TeV background when compared to the highly-boosted VHE emission from blazar cores [55].…”

“…The detection of extended X-ray emission from the large-scale jets in AGN by Chandra 4 has raised the possibility that these jets are also steady sources of VHE γ-rays. Electron synchrotron radiation is by now the favoured interpretation for the X-ray emission [e.g., 55,69], indicating the presence of highly energetic electrons with Lorentz factors up to γ ∼ 10 8 (100 µG/B) 1/2 D −1/2 , where D is the Doppler factor and B the large-scale magnetic field strength. While diffusive shock acceleration in the jet could in principle facilitate such energies, localized (shock-type) acceleration at knots is usually not sufficient given the fact that there is little evidence for e.g.…”

Particle Acceleration in Shearing Flows: Efficiencies and Limits

“…suggesting that electron Lorentz factors γ e ∼ (10 8 −10 9 ) are in principle achievable in the large-scale jets of AGN. This would provide support to the electron synchrotron interpretation of extended X-ray emission in AGN jets that requires to sustain ultra-relativistic electrons along the jet (e.g., Harris & Krawczynski 2006;Georganopoulos et al 2016). Note that for a Kraichnantype turbulence (α = 1/2), the numerical value, eq.…”

Active Galactic Nuclei: Boon or Bane for Biota?

“…For galaxies with black holes on the order of 10 4 to 10 5 M (Chilingarian et al 2018;Mezcua et al 2018;Graham et al 2019), these zones could be truncated at sub-pc scales; in comparison, note that the Bondi radius for Sagittarius A* is around 0.04 pc (Yuan & Narayan 2014). At sub-pc distances, planets may perhaps be subject to complex interactions with the dusty torus as well as strong outflows and winds from the accretion disc (Georganopoulos et al 2016;Gravity Collaboration 2018;Blandford et al 2018). Hence, close-in planets and moons at 1 pc might become uninhabitable from continual exposure to hot gas at relativistic speeds.…”