Related papers: Optical Spectroscopy of Blazars for the Cherenkov …
AGNs are believed to be the source of very energetic cosmic rays which, in turn, produce gamma rays throughout the interactions with matter. Therefore, the study of their very-high-energy (VHE) gamma-ray spectra is fundamental to understand…
The emission of very-high-energy photons (VHE, E$>$100 GeV) in active galactic nuclei (AGN) is closely connected with the production of ultra-relativistic particles. Among AGN, the subclass of extreme BL Lacertae are of particular interest…
Blazars are active galactic nuclei (AGN) with a relativistic jet oriented toward the observer. This jet is composed of accelerated particles which can display emission over the entire electromagnetic spectrum. Spectral variability has been…
The vast majority of extragalactic sources detected in the very high energy (E> 100 GeV) domaine are active galactic nuclei (AGN) located at cosmological distances. During their travel towards Earth, the emitted gamma-rays suffer from…
Active galactic Nuclei (AGNs) with their relativistic jets pointed toward the observer, are a class of luminous gamma-ray sources commonly known as blazars. The study of this source class is essential to unveil the physical processes…
The prospects for future blazar surveys by next-generation very high energy (VHE) gamma-ray telescopes, such as Advanced Gamma-ray Imaging System (AGIS) and Cherenkov Telescope Array (CTA), are investigated using the latest model of blazar…
The High Energy Stereoscopic System (H.E.S.S.) experiment, a ground-based gamma-ray Cherenkov telescope array located in Namibia, has now detected many extragalactic objects, which redshifts range from z=0.00183 up to z=0.2, possibly more.…
The emission of very-high-energy photons (VHE, E>100 GeV$) in blazars is closely connected to the production of ultra-relativistic particles and the role of these gamma-ray sources as cosmic particle accelerators. This work focuses on a…
The first three months of sky-survey operation with the Fermi Gamma Ray Space Telescope (Fermi) Large Area Telescope (LAT) reveals 132 bright sources at |b|>10 deg with test statistic greater than 100 (corresponding to about 10 sigma). Two…
The extragalactic high-energy $\gamma$-ray sky is dominated by blazars, which are active galactic nuclei with their jets pointing towards us. Distance measurements are of fundamental importance yet for some of these sources are challenging…
VERITAS is one of the world's most sensitive detectors of astrophysical VHE (Very High Energy; E > 100 GeV) gamma rays. This array of four 12-m imaging atmospheric-Cherenkov telescopes has operated for ~10 years, and nearly 5000 hours of…
We have searched for very high energy (VHE) gamma rays from four blazars using the CANGAROO-III imaging atmospheric Cherenkov telescope. We report the results of the observations of H 2356-309, PKS 2155-304, PKS 0537-441, and 3C 279,…
Active Galactic Nuclei (AGN) are now known to be strong gamma-ray emitters. After briefly describing the different classes of AGN and the basic tenets of unified schemes, I discuss the role of blazars (that is BL Lacs and flat-spectrum…
The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The Second LAT AGN Catalog (2LAC) includes 1017 gamma-ray sources located at high…
In this paper, we review the prospects for studies of active galactic nuclei (AGN) using the envisioned future Cherenkov Telescope Array (CTA). This review focuses on jetted AGN, which constitute the vast majority of AGN detected at…
Active Galactic Nuclei can be copious extragalactic emitters of MeV-GeV-TeV gamma rays, a phenomenon linked to the presence of relativistic jets powered by a super-massive black hole in the center of the host galaxy. Most of gamma-ray…
The VERITAS array of 12-m atmospheric-Cherenkov telescopes in southern Arizona is one of the world's most-sensitive detectors of very-high-energy (VHE, E>100 GeV) gamma rays. More than 50 extragalactic sources are known to emit VHE photons;…
The VERITAS array of four 12-m imaging atmospheric-Cherenkov telescopes began full-scale operations in 2007, and is one of the world's most sensitive detectors of astrophysical very high energy (VHE; E>100 GeV) gamma rays. Observations of…
In the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about…
The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains 2863 objects located at high Galactic latitudes (|b|>10{\deg}).…