High-Energy Aspects of Astrophysical Jets

Abstract

Various aspects of the high-energy emission from relativistic jets associated with compact astrophysical systems are reviewed. The main leptonic and hadronic processes responsible for the production of high-energy γ-rays, very-high energy neutrinos and ultra-high energy cosmic rays are discussed. Relations between the γγ pair production and photomeson production opacities are derived, and their consequences for the relative emission of γ-rays and neutrinos are examined. The scaling of the size and location of the various emission zones and other quantities with black hole mass and dimensionless luminosity is elucidated. The results are applied to individual classes of objects, including blazars, microquasars and gamma-ray bursts. It is concluded that if baryons are present in the jet at sufficient quantities, then under optimal conditions most systems exhibiting relativistic jets may be detectable by upcoming neutrino telescopes. An exception is the class of TeV blazars, for which γ-ray observations imply neutrino yields well below detection limit.

Hydrodynamic Collimation of Relativistic Outflows: Semianalytic Solutions and Application to Gamma‐Ray Bursts

“…The photon distribution produced inside those shocks is likely to have a nonthermal extension at high energies owing to multiple Compton scattering on the converging flow (a relativistic version of the Blandford Pyne process). If the shocks are produced at a modest optical depth then the nonthermal photons may escape before being thermalized, giving rise to a nonthermal spectral component of the prompt GRB emission, as proposed earlier (e.g., Eichler 1994;Levinson 2006b, and references therein). Detailed calculations are required to assess whether this process can indeed explain the observed spectra.…”

“…Opacity arguments suggest that the rapid variability of the TeV emission observed in the TeV blazars implies high Doppler factors of the emitting plasma in the γ-ray emission zone (e.g., Levinson 2006b). Such high values of the Doppler factor are in clear disagreement with the much lower values inferred from radio observations (e.g., Urry & Padovani 1991;Marscher 1999;Jorstad et al 2001).…”

Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy

“…While inner engines will still remain unresolved with future Cherenkov telescope arrays, microquasar jets and their interaction with the ISM might become resolvable, leading to the distinction of emission from the central object (which may be variable) and from the jet-ISM interaction (which may be stable). Microquasars, gamma-ray, and X-ray binaries, and high-energy aspects of astrophysical jets and binaries are discussed in [25].…”

Hadronic models of blazars require a change of the accretion paradigm

“…The adopted values of L acc and M for all sources studied here are given in Table 1. B13 give the jet power 1 estimated using the energy content and for one jet only, see their equations (3-5). However, the jet power, P j , is the enthalpy flux (e.g., Levinson 2006), and the counterjet should be included in the energy budget. Thus, we multiply their values by 8/3, assuming the protons are relativistic (and thus their 1 The entry for L p (the power in protons) of OJ 287 in B13 is a typo, it should be 0.083 rather than 8.3.…”