Active extragalactic sources - Nearly simultaneous observations from 20 centimeters to 1400 A

Signature of inverse Compton emission from blazars

“…Landau et al 1986;Massaro et al 2004; with fixed Galactic absorption. It is characterized by a normalization k, spectral index α, transition energy E1 and curvature parameter β.…”

“…The model has often been invoked to fit the entire SED of blazars (e.g. Landau et al 1986;Massaro et al 2004;Chen et al 2014) and such curved spectra of blazars are known to arise due to log parabolic electron distributions (e.g. Tramacere et al 2007Tramacere et al ,2009Paggi et al 2009).…”

The Blazar Paradigm: Synchro-Compton Emission from Relativistic Jets

“…As is discussed below, rapid-in many cases intraday-variability at low frequencies is difficult to reconcile with incoherent synchrotron radiation. Furthermore, it is rare in compact sources that the spectrum can be fit by a power law over more than a decade in frequency; the continuity of the spectra from radio to infrared does, however, suggest strongly that the infrared emission mechanism is the same as in the radio (Landau et al 1986). Independent evidence for the paradigm comes from Readhead (1994), who has found that the brightness temperatures of large samples of compact radio sources seem to obey a brightness temperature limit corresponding to equipartition in energy between the electrons and the magnetic field, as would only occur if the assumption that the radiation is incoherent synchrotron is valid.…”

0.35-3.5 micron photometry of blazars

“…have photon spectra which are significantly curved, steepening toward higher frequencies (see, for example, Landau et al 1986). Such curvature can be explained if the sources are inhomogeneous; the rate of steepening is related to the shape of the emitting region, generally thought to be the cone or funnel of a relativistic jet and the variations in particle energies and magnetic field strength along it.…”

“…In its simplest form, the spectrum is nearly a power law with index a (with a defined as L v y 01 ) over a narrow frequency range, as expected for a parent population of particles (generally assumed to be electrons) whose energy spectrum is also a power law. In simple realistic models the spectra will turn down at low and high frequencies due to self-absorption, energy losses, and energy cutoffs in the particle population.While spectra have often been fit with such simple models, it has become increasingly clear that real sources Visiting Astronomer at the Mount Lemmon Observing Facility, operated by the University of Minnesota and the University of California at San Diego.Visiting Astronomer at Steward Observatory, operated by the University of Arizona.Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.Visiting Astronomer at the Infrared Telescope Facility, operated by the University of Hawaii under contract to the National Aeronautics and Space Administration.have photon spectra which are significantly curved, steepening toward higher frequencies (see, for example, Landau et al 1986). Such curvature can be explained if the sources are inhomogeneous; the rate of steepening is related to the shape of the emitting region, generally thought to be the cone or funnel of a relativistic jet and the variations in particle energies and magnetic field strength along it.…”