The blazar paradigm and its discontents .
Abstract
The standard blazar paradigm consists of a supermassive black hole that expels relativistic jets of magnetized plasma in our direction. This plasma entrains nonthermal synchrotron-emitting electrons that furthermore scatter internally-produced synchrotron photons as well as externally-produced photons from the accretion-disk, the broad-line region, and the infrared-emitting torus. This picture has been very successful in reproducing the two-humped blazar spectral energy distribution. Yet various discontents persist, including (1) ultra-short variability at TeV energies that is much shorter than the dynamical timescale across the black hole; (2) very-high energy (VHE; >100 GeV) radiation from FSRQs; (3) evidence for a hard spectral component in high-synchrotron peaked objects, found when deabsorbing the measured VHE spectrum using conventional extragalactic background light (EBL) models; (4) an unusual slowly varying class of BL Lac objects. Some of these problems can be resolved by introducing a hadronic component into the blazar paradigm, consistent with the hypothesis that blazars are sources of ultra-high energy cosmic rays. Gamma-ray observations with the Cherenkov Telescope Array and neutrino observations with IceCube will be important to test this hypothesis.
- Publication:
-
Memorie della Societa Astronomica Italiana
- Pub Date:
- 2015
- DOI:
- 10.48550/arXiv.1408.6453
- arXiv:
- arXiv:1408.6453
- Bibcode:
- 2015MmSAI..86...13D
- Keywords:
-
- radiation processes: nonthermal;
- gamma rays;
- Galaxy: active;
- jets;
- ultra-high energy cosmic rays;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 12 pages, 5 figures, proceedings for "High Energy Astrophysics in Southern Africa," Bloemfontein, New Free State, South Africa, 23-25 April, 2014