Related papers: Rapid VHE variability in blazars

We study the variability properties at radio frequencies of the jets thought to be typical of Active Galactic Nuclei, i.e. bulk Lorentz factor \Gamma ~ 10, and incoherent synchrotron emission. We assume that the radiating electrons are…

Supermassive black holes in the centers of galaxies are very common. They are known to rotate, accrete, spin down and eject highly relativistic jets; those jets pointed at us all seem to show a spectrum with two strong bumps, one in the TeV…

Blazars are highly variable, radio-loud active galactic nuclei with jets oriented at a small angle to the line of sight. The observed emission of these sources covers the whole electromagnetic spectrum from radio frequencies up to the high…

The blazars 3C 454.3, PKS 0537-441 and PKS 2155-304 are traditionally known to be among the most active sources of this class. They emit at all frequencies, up to the gamma-rays, and are good probes of multiwavelength nuclear variability.…

A detailed multi-epoch study of the broadband spectral behaviour of the very high energy (VHE) source, 1ES\,1011+496, provides us with valuable information regarding the underlying particle distribution. Simultaneous observations of the…

Supermassive black holes at the centre of active galactic nuclei power some of the most luminous objects in the Universe. Typically, very long baseline interferometric (VLBI) observations of blazars have revealed only funnel-like…

Blazars are the most abundant class of known extragalactic very-high-energy (VHE, E>100 GeV) gamma-ray sources. However, one of the biggest difficulties in investigating their VHE emission resides in their limited number, since less than 60…

Gamma-ray emitting blazars have been the targets of many recent or ongoing monitoring programmes. The resulting multi-wavelength data archives are ideal for studying the quiescent and variable behaviour of the blazar PKS 2155-304. Here,…

This article focuses on certain variability and emission characteristics of Active Galactic Nuclei (AGN), especially their radio-loud subset consisting of quasars, BL Lacs and $\gamma$-ray detected narrow-line Seyfert 1 galaxies, all of…

Since 2002 the VHE (>100 GeV) gamma-ray flux of the high-frequency peaked BL Lac PKS 2155-304 has been monitored with the High Energy Stereoscopic System (HESS). An extreme gamma-ray outburst was detected in the early hours of July 28, 2006…

Particle acceleration induced by fast magnetic reconnection may help to solve current puzzles related to the interpretation of the very high energy (VHE) and neutrino missions from AGNs and compact sources in general. Our general…

The radio galaxy M87 has recently been found to be a rapidly variable TeV emitting source. We analyze the implications of the observed TeV characteristics and show that it proves challenging to account for them within conventional…

Blazars are very broadband cosmic sources with spectra spanning over twenty orders of magnitude in frequency, down to the 100 MHz regime in the radio range, up to VHE at several tens of TeV. The modelling of their spectral energy…

PKS 1510-089 is one of the most variable blazars. Very high energy gamma ray emission from this source was observed by H.E.S.S. during March-April 2009 and by MAGIC from February 3 to April 3, 2012 quasi-simultaneously with multi-wavelength…

PG 1553+113 is one of the few blazars with a convincing quasi-periodic emission in the gamma-ray band. The source is also a very high-energy (VHE; >100 GeV) gamma-ray emitter. To better understand its properties and identify the underlying…

We discuss production of very high energy (VHE) gamma-rays in large scale extragalactic jets of FR I sources. Based on recent optical and X-ray observations of these objects we evaluate their VHE emission in a framework of one electron…

X-ray variability in Active Galactic Nuclei (AGN) is commonly analysed in terms of the Power Spectral Density (PSD). The break observed in the power spectrum can be interpreted as a characteristic X-ray variability time scale. Here we study…

Hard X-ray observations are crucial to study the non-thermal jet emission from high-redshift, powerful blazars. We observed two bright z>2 flat spectrum radio quasars (FSRQs) in hard X-rays to explore the details of their relativistic jets…

We propose a new model for the description of ultra-short flares from TeV blazars by compact magnetized condensations (blobs), produced when red giant stars cross the jet close to the central black hole. Our study includes a simple…

During the last year, six new Active Galactic Nuclei (AGN) have been discovered and studied by H.E.S.S. at Very High Energies (VHE). Some of these recent discoveries have been made thanks to new enhanced analysis methods and are presented…