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 X-Ray Surveys as Tools to Investigate the Cosmological Evolution of Quasars, BL Lac Objects and Clusters of Galaxies

1987 ◽  
Vol 124 ◽  
pp. 593-595
Author(s):  
Isabella M. Gioia ◽  
Tommaso Maccacaro ◽  
Anna Wolter
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Progress Report ◽  
Cosmological Evolution ◽  
Clusters Of Galaxies ◽  
Bl Lac Objects ◽  
X Ray ◽  
Basic Properties ◽  
Bl Lac ◽  
Einstein Observatory

We present a progress report on a major extension of the Einstein Observatory Medium Sensitivity Survey (MSS). The basic properties of the extragalactic sources identified with Active Galactic Nuclei (AGN) and clusters of galaxies are discussed. Results from previous work are briefly summarized.

Commission N°48: High Energy Astrophysics (Astrophysique Des Hautes Energies)

1988 ◽  
Vol 20 (1) ◽  
pp. 671-675
Author(s):  
C.J. Cesarsky ◽  
R.A. Sunyaev ◽  
G.W. Clark ◽  
R. Giacconi ◽  
Vin-Yue Qu ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Supernova Remnants ◽  
Cataclysmic Variables ◽  
Galactic Nuclei ◽  
High Energy ◽  
Clusters Of Galaxies ◽  
High Energy Astrophysics ◽  
X Ray ◽  
X Ray Binaries ◽  
Imaging Telescopes

The european X-ray observatory (EXOSAT), which was launched in 1983 and which finished operations in April 1986, has brought a rich harvest of results in the period 1984-1987, surveyed here. The EXOSAT payload consisted of three sets of instruments: two low energy imaging telescopes (LE:E<2 KeV), a medium-energy experiment (ME:E=l-50KeV) and a gas scintillation proportional counter (GSPC:E=2-20KeV). Over most of the energy range covered, EXOSAT was not more sensitive than its predecessor, the american EINSTEIN satellite. But the EINSTEIN satellite is far from having exhausted the treasures of the X-ray sky. And EXOSAT, thanks to its elliptical 90-hour orbit, had the extra advantage of being able to make long, continuous observations of interesting objects, lasting up to 72 hours. Thus, EXOSAT was very well suited for variability studies, and many of its most important findings are in this area. EXOSAT observations sample a vide range of astrophysical sources: X-ray binaries, cataclysmic variables and active stars; supernova remnants and the interstellar medium; active galactic nuclei, and clusters of galaxies. Among the highlights, let us mention:

scholarly journals A MULTI-WAVELENGTH STUDY OF LOW-REDSHIFT CLUSTERS OF GALAXIES. I. COMPARISON OF X-RAY AND MID-INFRARED SELECTED ACTIVE GALACTIC NUCLEI

2011 ◽  
Vol 729 (1) ◽  
pp. 22 ◽  
Author(s):  
David W. Atlee ◽  
Paul Martini ◽  
Roberto J. Assef ◽  
Daniel D. Kelson ◽  
John S. Mulchaey
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Clusters Of Galaxies ◽  
Mid Infrared ◽  
X Ray ◽  
Multi Wavelength

scholarly journals X-Rays from Active Galactic Nuclei

1983 ◽  
Vol 6 ◽  
pp. 491-498 ◽  
Author(s):  
A.C. Fabian
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
X Rays ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac

Recent X-ray observations of active galactic nuclei and Seyfert galaxies in particular are briefly reviewed. The application of the efficiency limit to rapidly varying luminous sources such as NGC 6814 is discussed. It is argued that the variability and probable MeV spectral turnover imply that most of the electrons which radiate the observed flux are only mildly relativistic. A possible link between the steep soft X-ray spectra and featureless optical continua of BL Lac objects is considered.

scholarly journals Variable jet Lorentz factors can explain soft self-absorbed radio spectra of accreting black holes

2019 ◽  
Vol 489 (1) ◽  
pp. L58-L62
Author(s):  
Andrzej A Zdziarski
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Viewing Angle ◽  
Bl Lac Objects ◽  
X Ray ◽  
Black Hole Binaries ◽  
Hard State ◽  
Doppler Factor ◽  
Quasars And Radio Galaxies

Abstract We study the effect of variable jet bulk Lorentz factors, i.e. either jet acceleration or deceleration, on partially synchrotron self-absorbed radio spectra from cores of radio-loud active galactic nuclei and black hole binaries in the hard state. In about a half of quasars and radio galaxies, their core radio spectra are observed to be soft, i.e. have the spectral index of α < 0. If they are emitted by jets with constant Lorentz factors, that softness implies deposition of large amounts of energy at large distances from the centre. We show here that such soft spectra can be explained without that energetic requirement by emission of jets with the Doppler factor increasing with the distance. This can happen for either jet acceleration or deceleration, depending on the jet viewing angle. We find our model can explain the quiescent radio to X-ray spectra of the BL Lac objects Mrk 421 and Mrk 501.

scholarly journals The All-Sky Extragalactic X-Ray Foreground

1990 ◽  
Vol 123 ◽  
pp. 451-455
Author(s):  
Elihu Boldt
Keyword(s):  
Active Galactic Nuclei ◽  
Large Scale ◽  
Local Group ◽  
Galactic Nuclei ◽  
Clusters Of Galaxies ◽  
X Ray ◽  
Local Space ◽  
Dipole Analysis ◽  
Statistical Sample ◽  
Compact Sources

Observations of galaxies in the IR and optical (Lynden-Bell et al. 1989) suggest that the 600 km/s peculiar velocity of the LG (Local Group of galaxies) arises mainly from a foreground of anisotropically distributed mass within z = 0.013 (i.e., HR < 4000 km/s). Since the X-ray luminosity of bright extragalactic X-ray sources provides a good mass measure of the radiating objects involved and can be observed relatively free of galactic obscuration effects, such sources are likely candidates for serving as reliable tracers of the total underlying mass (i.e., dark as well as visible) responsible for the acceleration of the LG. In this connection, we note that the local gravitational dipole implied by the fifty X-ray brightest clusters of galaxies at z > 0.013 considered by Lahav et al. (1989) is relatively small compared with that inferred from the only three clusters at lower redshifts. Since the local space density of AGN (Active Galactic Nuclei) is about two orders of magnitude greater than rich clusters, however, such compact sources have the potential of providing a vastly improved statistical sample for tracing mass in the low-redshift region of particular interest. Furthermore, recent dipole analysis of the X-ray flux from bright AGN observed with HEAO-1 A2 indicates that they are indeed strong tracers of this matter (Miyaji and Boldt 1990). The implications of this for the very pronounced large-scale foreground anisotropies to be measured via low-redshift AGN resolved in more sensitive all-sky surveys are explored.

scholarly journals X-Ray Variability of Active Galactic Nuclei

1983 ◽  
Vol 6 ◽  
pp. 499-503 ◽  
Author(s):  
Daniel A. Schwartz ◽  
Greg Madejski ◽  
William H.-M. Ku
Keyword(s):  
Active Galactic Nuclei ◽  
Time Scales ◽  
Galactic Nuclei ◽  
Active Galaxies ◽  
X Rays ◽  
Active Nucleus ◽  
Massive Black Hole ◽  
Bl Lac Objects ◽  
X Ray ◽  
Structural Length

X-ray variability of active galactic nuclei is commonplace on scales from days to years. It also occurs, although rarely, on time scales as short as 200 seconds. Both these statements must be strongly qualified by the irregularity and insensitivity of the available observations. In the X-rays we expect that we are seeing deep within the active nucleus, near what is usually taken to be a massive black hole. The X-ray variability time scales may then give us the fundamental structural length scales. We would like to review data on active galaxies, present our new data on Einstein observations of BL Lac objects, and discuss all these in terms of a statistical quantification of the observations.

scholarly journals High-Resolution Observations of the M81 Nucleus

1989 ◽  
Vol 134 ◽  
pp. 513-514
Author(s):  
William C. Keel
Keyword(s):  
High Resolution ◽  
Active Galactic Nuclei ◽  
Radio Source ◽  
Galactic Nuclei ◽  
Line Spectrum ◽  
Narrow Line ◽  
Early Type ◽  
X Ray

The nucleus of the nearby Sb galaxy M81 has been shown to exhibit many of the features prominent in luminous active galactic nuclei: a variable, compact VLBI radio source (Kellermann et al. 1976, Jones, Sramek and Terzian 1981), a central variable X-ray source (Elvis and van Speybroeck 1982, Fabbiano 1988), and broad wings of Balmer emission similar in extent to those typical to Seyfert 1 nuclei (Peimbert and Torres-Peimbert 1981, Shuder and Osterbrock 1981). The nucleus also shows a narrow-line spectrum in many ways typical of LINERs (Heckman 1980), now known to be representative of early-type spiral nuclei in general.

Polarization Variability of Active Galactic Nuclei and X‐Ray Binaries

1997 ◽  
Vol 487 (1) ◽  
pp. 142-152 ◽  
Author(s):  
Gang Bao ◽  
Petr Hadrava ◽  
Paul J. Wiita ◽  
Ying Xiong
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
X Ray ◽  
X Ray Binaries
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