A FRAMEWORK FOR INTERPRETING OBSERVED PHENOMENA ASSOCIATED WITH RELATIVISTIC OUTFLOWS IN AGN

2008 ◽  
Vol 17 (09) ◽  
pp. 1521-1530 ◽  
Author(s):  
D. C. GABUZDA
Keyword(s):  
Active Galactic Nuclei ◽  
Circular Polarization ◽  
Faraday Rotation ◽  
Surrounding Medium ◽  
Galactic Nuclei ◽  
High Energy ◽  
Electromagnetic Current ◽  
Relativistic Jets ◽  
Relativistic Shocks ◽  
Abundant Evidence

A growing number of jets in active galactic nuclei (AGN) show clear signs of helical magnetic (B) fields: Faraday-rotation gradients across the VLBI jets, extended regions of jet with orthogonal B fields, transverse polarization and total-intensity structures characteristic of helical fields, interknot polarization implying underlying orthogonal B fields, and a predominance of orthogonal B fields in the VLBI cores. In addition, a link has now been found between the circular polarization detected in AGN cores and the presence of helical jet B fields within these cores. This now abundant evidence compels us to take very seriously the idea that many, possibly all, AGN jets have helical B fields. As a whole, the recent observational results considered here suggest that we must look at AGN jets as fundamentally electromagnetic, current-carrying structures if we wish to fully understand their nature. This provides an overall framework for interpreting various observed phenomena associated with the relativistic jets of AGN, including high-energy phenomena. Superposed on the structure of the underlying helical B field may be the effects of relativistic shocks and interaction with the surrounding medium in some cases; these may dominate observed phenomena locally, while it is the "intrinsic" helical B field of the jet itself that determines the global observed characteristics of the jet.

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 Relativistic jets in Narrow-Line Seyfert 1

2010 ◽  
Vol 6 (S275) ◽  
pp. 176-177
Author(s):  
L. Foschini ◽  
E. Angelakis ◽  
G. Bonnoli ◽  
G. Calderone ◽  
M. Colpi ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
High Energy ◽  
Narrow Line ◽  
Relativistic Jets ◽  
Preliminary Results ◽  
New Class ◽  
Γ Ray ◽  
First Time

AbstractNarrow-Line Seyfert 1 (NLS1) class of active galactic nuclei (AGNs) is generally radio-quiet, but a small percent of them are radio-loud. The recent discovery by Fermi/LAT of high-energy γ-ray emission from 4 NLS1s proved the existence of relativistic jets in these systems. It is therefore important to study this new class of γ-ray emitting AGNs. Here we report preliminary results about the observations of the July 2010 γ-ray outburst of PMN J0948+0022, when the source flux exceeded for the first time 10−6 ph cm−2 s−1 (E > 100 MeV).

scholarly journals Active Galactic Nuclei: Jets as the Source of Hadrons and Neutrinos

2014 ◽  
Vol 1 (1) ◽  
pp. 269-273
Author(s):  
Athina Meli ◽  
Paolo Ciarcelluti
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Cosmic Ray ◽  
High Energy ◽  
Plasma Jets ◽  
Shock Acceleration ◽  
Fermi Acceleration ◽  
Acceleration Mechanism ◽  
Relativistic Shocks

Active galactic nuclei are extragalactic sources, and their relativistic hot-plasma jets are believed to be the main candidates of the cosmic-ray origin, above the so-called knee region of the cosmic-ray spectrum. Relativistic shocks, either single or multiple, have been observed or been theorized to be forming within relativistic jet channels in almost all active galactic nuclei sources. The acceleration of non-thermal particles (e.g. electrons, protons) via the shock Fermi acceleration mechanism, is believed to be mainly responsible for the power-law energy distribution of the observed cosmic-rays, which in very high energies can consequently radiate high energy gamma-rays and neutrinos, through related radiation channels. Here, we will focus on the primary particle (hadronic) shock acceleration mechanism, and we will present a comparative simulation study of the properties of single and multiple relativistic shocks, which occur in AGN jets. We will show that the role of relativistic (quasi-parallel either quasi-perpendicular) shocks, is quite important since it can dramatically alter the primary CR spectral indices and acceleration eciencies. These properties being carried onto gamma-ray and neutrino radiation characteristics, makes the combination of them a quite appealing theme for relativistic plasma and shock acceleration physics, as well as observational cosmic-ray, gamma-ray and neutrino astronomy.

scholarly journals Particle-in-Cell Simulations of Astrophysical Relativistic Jets

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 450
Author(s):  
Athina Meli ◽  
Ken-ichi Nishikawa
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Relativistic Jets ◽  
High Energy Astrophysics ◽  
Jet Interaction ◽  
Particle In Cell ◽  
Electron Positron ◽  
Kinetic Instabilities

Astrophysical relativistic jets in active galactic nuclei, gamma-ray bursts, and pulsars is the main key subject of study in the field of high-energy astrophysics, especially regarding the jet interaction with the interstellar or intergalactic environment. In this work, we review studies of particle-in-cell simulations of relativistic electron–proton (e−−p+) and electron–positron (e±) jets, and we compare simulations that we have conducted with the relativistic 3D TRISTAN-MPI code for unmagnetized and magnetized jets. We focus on how the magnetic fields affect the evolution of relativistic jets of different compositions, how the jets interact with the ambient media, how the kinetic instabilities such as the Weibel instability, the kinetic Kelvin–Helmholtz instability and the mushroom instability develop, and we discuss possible particle acceleration mechanisms at reconnection sites.

scholarly journals POWERFUL RELATIVISTIC JETS IN SPIRAL GALAXIES

2012 ◽  
Vol 08 ◽  
pp. 172-177 ◽  
Author(s):  
LUIGI FOSCHINI
Keyword(s):  
Active Galactic Nuclei ◽  
Spiral Galaxies ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
High Energy ◽  
Narrow Line ◽  
Relativistic Jets ◽  
Accretion Rates ◽  
Γ Rays ◽  
Eddington Limit

The discovery of high-energy (E > 100 MeV) γ rays from Narrow-Line Seyfert 1 Galaxies (γ-NLS1s) has confirmed the presence of powerful relativistic jets in this class of active galactic nuclei (AGN). Although the jet emission is similar to that of blazars and radio galaxies, γ-NLS1s have some striking differences: relatively small masses (106-8 M⊙), high accretion rates (0.1-1 times the Eddington limit) and are generally hosted by spiral galaxies. It is now possible to study a rather unexplored range of mass and accretion rates of AGN with relativistic jets. Specifically, in this work I present some results obtained by comparing a sample of blazars and γ-NLS1s with another sample of Galactic binaries with relativistic jets (stellar mass black holes and neutron stars).

scholarly journals Extragalactic shocks as cosmic accelerators

2006 ◽  
Vol 2 (14) ◽  
pp. 95-96
Author(s):  
Mikhail V. Medvedev
Keyword(s):  
Active Galactic Nuclei ◽  
Large Scale ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Maximum Energy ◽  
Shock Acceleration ◽  
Fermi Acceleration ◽  
High Energy Cosmic Rays ◽  
Relativistic Shocks

AbstractIt is quite well established that shocks accelerate particles via the Fermi mechanism. We discuss common features of various extragalactic sources, ranging from Gamma-Ray Bursts and jets of Active Galactic Nuclei to Large-Scale Structure shocks and address how they affect particle acceleration. In particular, we address constraints on the maximum energy of ultra-high-energy cosmic rays. Interestingly, some recent studies indicate that Fermi acceleration in relativistic shocks (and GRBs, in particular) faces severe difficulties. We will address this issue and demonstrate that the ‘observed’ shock acceleration of electrons may have nothing to do with Fermi acceleration, but may rather be associated with micro-physics of collisionless shocks.

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