scholarly journals Radio Galaxies at VHE Energies

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 116 ◽  
Author(s):  
Frank Rieger ◽  
Amir Levinson
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Concise Overview ◽  
Recent Developments ◽  
Γ Ray ◽  
Very High

Radio Galaxies have by now emerged as a new γ-ray emitting source class on the extragalactic sky. Given their remarkable observed characteristics, such as unusual gamma-ray spectra or ultrafast VHE variability, they represent unique examples to probe the nature and physics of active galactic nuclei (AGN) in general. This review provides a compact summary of their observed characteristics at very high γ-ray energies (VHE; greater than 100 GeV) along with a discussion of their possible physics implications. A particular focus is given to a concise overview of fundamental concepts concerning the origin of variable VHE emission, including recent developments in black hole gap physics.

M 87 — TEN YEARS OF TEV GAMMA-RAY OBSERVATIONS

2010 ◽  
Vol 19 (06) ◽  
pp. 849-857
Author(s):  
MATTHIAS BEILICKE
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Radio Galaxy ◽  
Galactic Nuclei ◽  
Plasma Jet ◽  
Radio Galaxies ◽  
Jet Physics ◽  
X Ray ◽  
High Energies ◽  
Very High

The giant radio galaxy M 87 is located 16.7 Mpc away and harbours a supermassive black hole in its center. Structures of its relativistic plasma jet are resolved at radio, optical and X–ray energies. M 87 belongs to the class of active galactic nuclei and is one of only a few radio galaxies detected at very-high energies (E > 100 GeV ). This makes it a unique laboratory to study jet physics and the corresponding emission processes. The results obtained from TeV gamma-ray observations during the last decade are discussed.

scholarly journals HIGH-ENERGY EMISSION FROM JET–CLOUD INTERACTIONS IN AGNs

2010 ◽  
Vol 19 (06) ◽  
pp. 931-936 ◽  
Author(s):  
ANABELLA T. ARAUDO ◽  
VALENTÍ BOSCH-RAMON ◽  
GUSTAVO E. ROMERO
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Line Emission ◽  
Galactic Nuclei ◽  
Small Region ◽  
High Energy ◽  
Energy Emission ◽  
Central Regions ◽  
High Energy Emission

Active galactic nuclei present continuum and line emission. The emission lines are originated by gas located close to the central supermassive black hole. Some of these lines are broad, and would be produced in a small region called broad-line region. This region could be formed by clouds surrounding the central black hole. In this work, we study the interaction of such clouds with the base of the jets in active galactic nuclei, and we compute the produced high-energy emission. We focus on sources with low luminosities in the inner jet regions, to avoid strong gamma-ray absorption. We find that the resulting high-energy radiation may be significant in Centaurus A. Also, this phenomenon might be behind the variable gamma-ray emission detected in M87, if very large dark clouds are present. The detection of jet–cloud interactions in active galactic nuclei would give information on the properties of the jet base and the very central regions.

scholarly journals Similarity and diversity of black holes - view from the Very High Energies

2016 ◽  
Vol 12 (S324) ◽  
pp. 11-18
Author(s):  
Elina Lindfors
Keyword(s):  
Black Holes ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Mass Scale ◽  
Relativistic Jets ◽  
Very High Energy ◽  
Energy Gamma ◽  
Very High

AbstractActive galactic nuclei, hosting supermassive black holes and launching relativistic jets, are the most numerous objects on the gamma-ray sky. At the other end of the mass scale, phenomena related to stellar mass black holes, in particular gamma-ray bursts and microquasars, are also seen on the gamma-ray sky. While all of them are thought to launch relativistic jets, the diversity even within each of these classes is enormous. In this review, I will discuss recent very high energy gamma-ray results that underline both the similarity of the black hole systems, as well as their diversity.

scholarly journals Radio Galaxies at TeV Energies: Preface

Galaxies ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 18
Author(s):  
Dorit Glawion
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Plasma Jets ◽  
Line Of Sight ◽  
Spectral Features ◽  
Viewing Angle ◽  
Special Issue ◽  
Key Aspects

The majority of the known extragalactic sky from TeV gamma-ray energies consists of blazars having plasma jets pointing in the direction of the line-of-sight, which results in a large Doppler boosting of their emission. Up to now, only six galaxies with a larger viewing angle have been detected in the TeV range. These objects also show fascinating properties, such as fast variability or spectral features and are called “radio galaxies”. The TeV radio galaxies provide a unique laboratory for studying key aspects of active galactic nuclei. This Special Issue of Galaxies targets these exciting objects.

scholarly journals Radio and Gamma-ray emission in nearby BL Lacs

2013 ◽  
Vol 9 (S304) ◽  
pp. 200-203 ◽  
Author(s):  
G. Giovannini ◽  
E. Liuzzo ◽  
B. Boccardi ◽  
M. Giroletti
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Scale Structure ◽  
Bl Lac Objects ◽  
Long Baseline ◽  
Γ Ray ◽  
Gamma Ray Emission ◽  
Very Long Baseline Array ◽  
Bl Lacs

AbstractThe advent of Fermi is changing our understanding on the radio and γ-ray emission in active galactic nuclei. Unlike pre-Fermi ideas, BL Lac objects are found to be the most abundant emitters in the γ-ray band. However, since they are relatively weak radio sources, most of their parsec-scale structure and their multifrequency properties are poorly understood and/or have not been investigated in a systematic fashion. Here we are analyzing the radio and γ-ray emission properties of a sample of 42 BL Lacs selected with no constraint on their radio and γ-ray emission. Thanks to new Very Long Baseline Array observations at 8 and 15 GHz for the whole sample, we discuss their parsec-scale structure. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. The comparison between our results in radio and gamma-ray bands points out the presence of a large number of faint BL Lacs showing “non-classical” properties such as low source compactness, low core dominance, no gamma-ray emission.

Very High Energy γ-rays from AGN

2002 ◽  
Vol 19 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Tadashi Kifune
Keyword(s):  
Electromagnetic Radiation ◽  
Active Galactic Nuclei ◽  
Energy Band ◽  
Galactic Nuclei ◽  
High Energy ◽  
Current Status ◽  
Very High Energy ◽  
Γ Rays ◽  
Γ Ray ◽  
Very High

AbstractEvidence of TeV γ-ray emission has been found for only a handful of active galactic nuclei, with detailed investigations limited to the blazars Mrk 421 and Mrk 501. TeV γ-ray astronomy, as the highest energy band, provides important information that is hard to obtain from longer wavelength electromagnetic radiation. The current status of TeV γ-ray studies of active galactic nuclei is summarized and our understanding of the high energy phenomena taking place in active galactic nuclei is outlined, with the prospects for future TeV γ-ray observations also considered.

scholarly journals GRAVITATIONAL SHOCKS AS A KEY INGREDIENT OF GAMMA-RAY BURSTS

2012 ◽  
Vol 27 (20) ◽  
pp. 1250110
Author(s):  
ANASTASIOS AVGOUSTIDIS ◽  
RAUL JIMENEZ ◽  
LUIS ÁLVAREZ-GAUMÉ ◽  
MIGUEL A. VÁZQUEZ-MOZO
Keyword(s):  
Numerical Simulations ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Initial Conditions ◽  
Strong Field ◽  
Galactic Nuclei ◽  
Relevant Parameter ◽  
Supernova Explosions ◽  
Γ Ray ◽  
Neutron Core

We identify a novel physical mechanism that may be responsible for energy release in γ-ray bursts. Radial perturbations in the neutron core, induced by its collision with collapsing outer layers during the early stages of supernova explosions, can trigger a gravitational shock, which can readily eject a small but significant fraction of the collapsing material at ultra-relativistic speeds. The development of such shocks is a strong-field effect arising in near-critical collapse in general relativity and has been observed in numerical simulations in various contexts, including, in particular, radially perturbed neutron star collapse, albeit for a tiny range of initial conditions. Therefore, this effect can be easily missed in numerical simulations if the relevant parameter space is not exhaustively investigated. In the proposed picture, the observed rarity of γ-ray bursts would be explained if the relevant conditions for this mechanism appear in only about one in every 104–105 core collapse supernovae. We also mention the possibility that near-critical collapse could play a role in powering the central engines of active galactic nuclei.

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