Enhanced shock acceleration in relativistic jets and cosmic ray origin in active galactic nuclei

Nature ◽  
1989 ◽  
Vol 342 (6250) ◽  
pp. 654-656 ◽  
Author(s):  
J. J. Quenby ◽  
R. Lieu
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
Relativistic Jets

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 Polarimetric Properties of Blazars Caught by the WEBT

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 42
Author(s):  
Claudia M. Raiteri ◽  
Massimo Villata
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Plasma Jets ◽  
Line Of Sight ◽  
Optical Behaviour ◽  
Relativistic Jets ◽  
Comprehensive Picture ◽  
Multi Wavelength ◽  
Extreme Variability ◽  
Continuous Range

Active galactic nuclei come in many varieties. A minority of them are radio-loud, and exhibit two opposite prominent plasma jets extending from the proximity of the supermassive black hole up to megaparsec distances. When one of the relativistic jets is oriented closely to the line of sight, its emission is Doppler beamed and these objects show extreme variability properties at all wavelengths. These are called “blazars”. The unpredictable blazar variability, occurring on a continuous range of time-scales, from minutes to years, is most effectively investigated in a multi-wavelength context. Ground-based and space observations together contribute to give us a comprehensive picture of the blazar emission properties from the radio to the γ-ray band. Moreover, in recent years, a lot of effort has been devoted to the observation and analysis of the blazar polarimetric radio and optical behaviour, showing strong variability of both the polarisation degree and angle. The Whole Earth Blazar Telescope (WEBT) Collaboration, involving many tens of astronomers all around the globe, has been monitoring several blazars since 1997. The results of the corresponding data analysis have contributed to the understanding of the blazar phenomenon, particularly stressing the viability of a geometrical interpretation of the blazar variability. We review here the most significant polarimetric results achieved in the WEBT studies.

The GLEAM 4-Jy Sample: The brightest radio-sources in the southern sky

2019 ◽  
Vol 15 (S356) ◽  
pp. 375-375
Author(s):  
Sarah White
Keyword(s):  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Visual Inspection ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Relativistic Jets ◽  
The Galaxy ◽  
Murchison Widefield Array ◽  
Past Activity

AbstractLow-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few “radio-loud” galaxies for robust studies in terms of redshift-evolution and/or environment. Hence our use of new observations from the Murchison Widefield Array (the SKA-Low precursor), over the southern sky, to construct the GLEAM 4-Jy Sample (1,860 sources at S151MHz > 4 Jy). This sample is dominated by AGN and is 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S178MHz > 10 Jy) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way galaxies evolve, we first need to correctly identify the galaxy hosting the radio emission. This has now been completed for the GLEAM 4-Jy Sample – through repeated visual inspection and extensive checks against the literature – forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment.

Relativistic Jets in Active Galactic Nuclei

2014 ◽  
Author(s):  
Geoffrey Bicknell ◽  
Mohammad Nawaz ◽  
Alexander Wagner ◽  
Masayuki Umemura ◽  
Brian McNamara ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Relativistic Jets

scholarly journals Intrinsic physical conditions and structure of relativistic jets in active galactic nuclei

2015 ◽  
Vol 447 (3) ◽  
pp. 2726-2737 ◽  
Author(s):  
E. E. Nokhrina ◽  
V. S. Beskin ◽  
Y. Y. Kovalev ◽  
A. A. Zheltoukhov
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Relativistic Jets ◽  
Physical Conditions

scholarly journals High Resolution X-ray Spectroscopy of Active Galactic Nuclei

1990 ◽  
Vol 115 ◽  
pp. 262-273
Author(s):  
Julian H. Krolik
Keyword(s):  
High Resolution ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Light Sources ◽  
Clusters Of Galaxies ◽  
Relativistic Jets ◽  
Bl Lac Objects ◽  
X Ray ◽  
Interstellar Material ◽  
Scientific Value

AbstractHigh-resolution X-ray spectroscopy has the potential to reveal a number of interesting features of active galactic nuclei, primarily, though not exclusively, through the measurement of absorption lines. After a brief review of the principal problems of AGN research, selected potential high-resolution observations are discussed with a view toward assessing their scientific value and the degree of resolution they will require. Two classes of observations pertaining directly to AGNs are discussed: Fe Kα spectroscopy relevant to the dynamical and thermal character of the emission line zones; and measurement of resonance line absorption by highly-ionized species in BL Lac objects, which should tell us about entrainment of interstellar material by relativistic jets. A third class of potentially important observations uses AGNs as background light sources in order to directly measure the distance to clusters of galaxies.

scholarly journals On the radio image of relativistic jets – I. Internal structure, Doppler boosting, and polarization maps

2019 ◽  
Vol 488 (1) ◽  
pp. 224-233 ◽  
Author(s):  
A V Chernoglazov ◽  
V S Beskin ◽  
V I Pariev
Keyword(s):  
Active Galactic Nuclei ◽  
Internal Structure ◽  
Linear Polarization ◽  
Ambient Pressure ◽  
Galactic Nuclei ◽  
Synchrotron Emission ◽  
Relativistic Jets ◽  
Radio Image ◽  
Radial Profiles

ABSTRACT In this first paper from forthcoming series of works devoted to radio image of relativistic jets from active galactic nuclei the role of internal structure of a flow is discussed. We determine the radial profiles of all physical values for reasonable Michel magnetization parameter σM and ambient pressure Pext. Maps of Doppler boosting factor δ and observed directions of linear polarization of synchrotron emission are also constructed.

scholarly journals Relativistic Jets from Active Galactic Nuclei

2019 ◽  
Vol 57 (1) ◽  
pp. 467-509 ◽  
Author(s):  
Roger Blandford ◽  
David Meier ◽  
Anthony Readhead
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Hot Spot ◽  
Galactic Nuclei ◽  
Cosmic Ray ◽  
Major Influence ◽  
Buoyant Plumes ◽  
Normal Galaxies ◽  
Sphere Of Influence

The nuclei of most normal galaxies contain supermassive black holes, which can accrete gas through a disk and become active. These active galactic nuclei (AGNs) can form jets that are observed on scales from astronomical units to megaparsecs and from meter wavelengths to TeV energies. High-resolution radio imaging and multiwavelength/messenger campaigns are elucidating the conditions under which this happens. Evidence is presented that: ▪ Relativistic AGN jets are formed when the black hole spins and the the accretion disk is strongly magnetized, perhaps on account of gas accreting at high latitude beyond the black hole sphere of influence. ▪ AGN jets are collimated close to the black hole by magnetic stress associated with a disk wind. ▪ Higher-power jets can emerge from their galactic nuclei in a relativistic, supersonic, and proton-dominated state, and they terminate in strong, hot spot shocks; lower-power jets are degraded to buoyant plumes and bubbles. ▪ Jets may accelerate protons to EeV energies, which contribute to the cosmic ray spectrum and may initiate pair cascades that can efficiently radiate synchrotron γ-rays. ▪ Jets were far more common when the Universe was a few billion years old and black holes and massive galaxies were growing rapidly. ▪ Jets can have a major influence on their environments, stimulating and limiting the growth of galaxies. The observational prospects for securing our understanding of AGN jets are bright.

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