Related papers: Models of variability in blazar jets

Variations of the X-ray spectral slope have been found in many Active Galactic Nuclei (AGN) at moderate luminosities and redshifts, typically showing a "softer when brighter" behaviour. However, similar studies are not usually performed for…

We present a new time-dependent inhomogeneous jet model of non-thermal blazar emission, which reproduces the entire spectral energy distribution together with the rapid gamma-ray variability. Ultra-relativistic leptons are injected at the…

We collect a large sample with a reliable redshift detected by the Fermi satellite after 10 years of data (4FGL-DR2), including blazars, $\gamma$-ray Narrow-line Seyfert 1 galaxies ($\gamma$NLS1s), and radio galaxies. The spectral energy…

The theory of particle acceleration at shock fronts is briefly reviewed, with special emphasis on the production of the particles responsible for the nonthermal emission from blazars. The flat radio/IR spectra of these sources cannot be…

Blazars are a subclass of active galactic nuclei (AGN) that have a relativistic jet with a small viewing angle towards the observer. Recent results based on hadronic scenarios have motivated an ongoing discussion of how a blazar can produce…

Aims: We investigate the one-zone SSC model of TeV blazars in the presence of electron acceleration. In this picture electrons reach a maximum energy where acceleration saturates from a combination of synchrotron and inverse Compton…

We report on long-term multi-wavelength monitoring of blazar Mrk 421 by the GASP-WEBT collaboration and Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in the period 2007-2015, characterized by…

The synchrotron reflection scenario recently proposed to explain $\gamma$-ray flares observed from blazar jets is studied. Our analysis takes into account the angular distribution of the beamed radiation, the finite extent of the scattering…

We examine the implications of the recently proposed Geometric Masking scenario for the Active Galactic Nuclei (AGN) Unification Scheme, the blazar sequence, and broader blazar phenomenology, and evaluate its consistency with recent…

We describe the dynamical evolution of hot spots velocity, pressure and mass density in radio loud active galactic nuclei (AGNs), taking proper account of (1) the conservations of the mass, momentum, and kinetic energy flux of the unshocked…

We discuss acceleration measurements for a large sample of extragalactic radio jets from the MOJAVE program which studies the parsec-scale jet structure and kinematics of a complete, flux-density-limited sample of Active Galactic Nuclei…

We investigate the Fermi LAT gamma-ray and 15 GHz VLBA radio properties of a joint gamma-ray- and radio-selected sample of AGNs obtained during the first 11 months of the Fermi mission (2008 Aug 4 - 2009 Jul 5). Our sample contains the…

The aim of this short paper is to motivate and encourage research in the field of Active Galactic Nuclei (AGN). Here we summarize the main open questions concerning the central engine. Is the central black hole rapidly spinning and can we…

We use data from a recent long ASCA observation of the Narrow Line Seyfert 1 Ark 564 to investigate in detail its timing properties. We show that a thorough analysis of the time series, employing techniques not generally applied to AGN…

Context: Few Active Galactic Nuclei (AGN) reveal a double sided jet system. However, these are crucial to understand basic physical properties of extragalactic jets. Aims: We address the questions whether jets in AGN are symmetric in…

In next five years, dramatic progress is anticipated for the AGN studies, as we have two important missions to observe celestial sources in the high energy regime: GLAST and Suzaku. In this talk, I will summarize recent highlights in…

A common feature of Active Galactic Nuclei (AGN) is their random variations in brightness across the whole emission spectrum, from radio to $\gamma$-rays. Studying the nature and origin of these fluctuations is critical to characterising…

Some progress in understanding AGN variability is reviewed. Reprocessing of X-ray radiation to produce significant amounts of longer-wavelength continua seems to be ruled out. In some objects where there has been correlated X-ray and…

The multiwavelength spectrum of BL Lacertae during its July 1997 outburst is analyzed in terms of different variations of the homogeneous leptonic jet model for the production of high-energy radiation from blazars. We find that a…

We discuss the theory and implementation of statistically rigorous fits to synchrotron self Compton models for datasets obtained from multi-wavelength observations of active galactic nuclei spectral energy distributions. The methods and…