Nonthermal electron-positron pairs and cold matter in the central engines of active galactic nuclei

1992 ◽  
Author(s):  
Andrzej A. Zdziarski
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Nonthermal Electron ◽  
Electron Positron ◽  
Cold Matter

scholarly journals Inferring the jet parameters of active galactic nuclei using Bayesian analysis of VLBI data with a non-uniform jet model

2019 ◽  
Vol 488 (1) ◽  
pp. 939-953 ◽  
Author(s):  
Ilya N Pashchenko ◽  
Alexander V Plavin
Keyword(s):  
Bayesian Analysis ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Peak Frequency ◽  
Physical Parameters ◽  
Image Deconvolution ◽  
Long Baseline ◽  
Central Engine ◽  
Electron Positron ◽  
Vlbi Data

ABSTRACTThe physical parameters of the jets of active galactic nuclei observed with Very Long Baseline Interferometry (VLBI) are usually inferred from core-shift measurements or from the flux and size measured at the peak frequency of the synchrotron spectrum. Both methods are preceded by modelling the observed VLBI jet structure with simple Gaussian templates. Here we infer the jet parameters using an inhomogeneous jet model directly, bypassing the modelling of the source structure with a Gaussian template or image deconvolution. We apply Bayesian analysis to multifrequency VLBA observations of radio galaxy NGC 315 and find that its parsec-scale jet is well described by an inhomogeneous conical model. Our results favour an electron–positron jet. We also detect a component as a part of a counter jet. Its position implies the presence of an external absorber with a steep density gradient close (r = 0.1 pc) to the central engine.

scholarly journals Rapid X-ray variability in active galactic nuclei

1986 ◽  
Vol 119 ◽  
pp. 269-271 ◽  
Author(s):  
P. Barr ◽  
R. Mushotzky ◽  
P. Giommi ◽  
J. Clavel ◽  
W. Wamsteker
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Rapid Variability ◽  
X Ray ◽  
Electron Positron ◽  
Eddington Limit

SummaryRecent EXOSAT observations of active galactic nuclei are presented. Unlike earlier X-ray satellites (all of which flew in low earth orbit), the deep orbit of EXOSAT allows long continuous observations of celestial X-ray sources, uninterrupted by earth occultation etc. We present the results of EXOSAT observations of several AGN which have been seen to vary rapidly (timescale 0.2–6 hours). We also consider the implications of rapid variability in AGN. For Seyfert galaxies and quasars, we find a highly significant correlation between the timescale of variability and their X-ray luminosity. They are not, howwever, bounded either by the (classical) Eddington limit nor by efficiency arguments. We sugest, rather, that the emitting plasma is dominated by electron-positron pairs.

scholarly journals Physical Processes in Active Galactic Nuclei

1986 ◽  
Vol 89 ◽  
pp. 324-345
Author(s):  
Roland Svensson
Keyword(s):  
Pair Production ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Rest Mass ◽  
Galactic Nuclei ◽  
Nonthermal Plasma ◽  
Lorentz Factor ◽  
Analytical Models ◽  
Potential Wells ◽  
Electron Positron

AbstractActive galactic nuclei (AGNs) emit continuum radiation evenly spread over up to ten decades in frequency from the radio into the gamma-ray range. Plausible emission mechanisms and their characteristics are reviewed. In the deep potential wells around black holes the mean energy per proton can reach 100 MeV. Part or all of this energy may be channeled to all electrons equally (thermal plasma) or, preferentially, into only a small fraction of the electrons (nonthermal plasma). In the former case thermal Comptonization of soft photons may be the dominant emission mechanism, while in the latter case the synchrotron and the inverse Compton scattering process (synchro-self-Compton) are likely to dominate.When the compactness parameter L (hν≈mc2 )/R. (power L, radius R) exceeds about 1030 ergs cm−1s−1 or L>Lc ≡ 1030R ergs s−1, then electron-positron pair production takes place due to photon-photon interactions causing the source to shroud itself with an electron-positron atmosphere. The efficiency of pair cascades in converting injected energy into electron-positron rest mass can reach levels of about 10% in static pair atmospheres. The emerging radiation is strongly modified by the pair atmosphere causing the spectrum to soften and to have characteristic breaks.For emission coming from a region near the Schwarzschild radius, L>10-3LEdd is sufficient to cause prolific pair production. Radiation pressure then drives a mildly relativistic pair wind with Compton drag limiting the Lorentz factor to be less then 10. The pair rest mass power is at most of the order of Lc.Most results so far on static pair atmospheres and pair winds are either qualitative or based on simple analytical models. Needed numerical treatments of both time dependent and steady radiative transfer of both the continuum and the annihilation line radiation in mildly relativistic flows are relevant not only for AGNs but also for gamma ray bursts and galactic black hole sources.

scholarly journals The Electron-Positron Cauldron and the Formation of the Hard Radiation of Quasars and AGN

1986 ◽  
Vol 119 ◽  
pp. 383-393
Author(s):  
N.S. Kardashev ◽  
I.D. Novikov ◽  
B.E. Stern
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Physical Parameters ◽  
Physical Processes ◽  
Physical Conditions ◽  
Electron Positron ◽  
Hard Radiation ◽  
The Universe

Active Galactic Nuclei (AGN) and quasars have unique physical parameters among all the objects in the Universe. Undoubtedly it is the uniqueness of the physical conditions in these systems that gives rise to the peculiar physical processes in them.

scholarly journals Black Hole Models of Quasars

1986 ◽  
Vol 119 ◽  
pp. 359-369 ◽  
Author(s):  
R. D. Blandford
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Cosmic Time ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Massive Black Hole ◽  
Binary Black Holes ◽  
Electron Positron ◽  
Gas Supply

Observations of active galactic nuclei are interpreted in terms of a theoretical model involving accretion onto a massive black hole. Optical quasars and Seyfert galaxies are associated with holes accreting near the Eddington rate and radio galaxies with sub-critical accretion. It is argued that magnetic fields are largely responsible for extracting energy and angular momentum from black holes and disks. Recent studies of electron-positron pair plasmas and their possible role in establishing the emergent X-ray spectrum are reviewed. The main evolutionary properties of active galactic nuclei can be interpreted in terms of a simple model in which black holes accrete gas at a rate dictated by the rate of gas supply which decreases with cosmic time. It may be worth searching for eclipsing binary black holes in lower power Seyferts.

Sign in / Sign up

Export Citation Format

Share Document