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The X-Ray Spectra of Active Galactic Nuclei
Physica Scripta, 1984Recent observations of the X-ray spectra of active galactic nuclei are reviewed. After an outline of the properties of these sources deduced from observations at other wavelengths, the relevance of X-ray spectra to our understanding of the X-ray emission mechanisms and of the ultimate source of energy is discussed.
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The X-ray variability of active galactic nuclei
2008Recent results relating to the X-ray variability exhibited by active galactic nuclei are reviewed. EXOSAT observations have established, contrary to earlier indications, that X-ray variability on a timescale of an hour or less is a relatively common feature of such sources.
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X-Ray Timing and Spectral Observations of Active Galactic Nuclei
Space Science Reviews, 1985Over 500 galaxies with active nuclei (AGN), in which class are included Seyfert galaxies, radio galaxies, QSOs and BL Lacertid-type objects, have so far been detected at X-ray wavelengths. Most of these are faint objects for which the only information available is a flux obtained from an observation with the Einstein Observatory, but somewhere upwards ...
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Limits of X-ray variability in active galactic nuclei
Nature, 1986A significant correlation is demonstrataed here between the X-ray luminosity and the timescale of X-ray variability for Seyfert galaxies and quasars. This is interpreted as evidence that the emitting plasma is near the limit of being dominated by electron-positron pairs.
P. Barr, R. F. Mushotzky
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X-Ray Variability in Active Galactic Nuclei
1998X-ray variability is a distinguishing property of Active Galactic Nuclei (AGN), and the energetics and time scales of the emission dictate that the X-rays must originate very close to the central engine. In this review I discuss two basic topics from AGN variability research.
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X-Ray Spectra of Active Galactic Nuclei
1980There are a variety of galaxies which are classified as nuclearactive, ranging from those which have nuclei which are merely distinguishable from a stellar component all the way to QSO’s. The subject of this lecture will be only those extreme cases (Seyfert I, BL Lac and quasar) which constitute the most intense compact X-ray sources which are ...
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Obscured active galactic nuclei: the hidden side of the X–ray Universe
Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 2002Most active galactic nuclei (AGN) are 'obscured', i.e. the nucleus is hiding behind a screen of absorbing material. The advantage of having the nucleus obscured is to make easier the observations of those emission components which originate in circumnuclear matter outside the absorbing regions, because in this case they are not outshone by the nuclear ...
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Optical and X-Ray Properties of Active Galactic Nuclei
1994The discovery of nuclear activity in galaxies results from the pioneering work of Fathi, Slipher2 and Hubble3. The first found Active Galactic Nuclei (AGN), NGC1068, NGC4051 and NGC4151, displayed not only strong broad permittted emission hydrogen lines (such as Hβ λ4861) but also narrow forbidden ion emission lines, characteristic of well known ...
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The soft X-ray spectra of active galactic nuclei
2008EXOSAT LE and ME data on Seyfert 1 galaxies and quasars are reviewed: the observations indicate that a strong flux of soft X-rays, in excess of the power-law continuum that extends over most of the spectrum, is a common feature of the emission of Active Galactic Nuclei (AGN).
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