Results 191 to 200 of about 50,261 (220)

Obscured active galactic nuclei: the hidden side of the X–ray Universe

Philosophical Transactions Series A, Mathematical, Physical, and Engineering Sciences, 2002
Most 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 ...
G Matt
exaly   +6 more sources

X-ray timing studies of Active Galactic Nuclei

AIP Conference Proceedings, 2008
We present a power spectral analysis survey of 24 active galactic nuclei (AGN). We combine X‐ray observations to produce a power spectrum covering a broad range of Fourier frequencies and fit the power spectrum of each AGN using a single‐bend power‐law model.
I M Mᶜhardy, P Uttley, Ye-Fei Yuan
exaly   +2 more sources

X-rays from active galactic nuclei ? Hard component

Space Science Reviews, 1981
It is now well known that X-ray emission in active galactic nuclei (AGN) is a fairly common phenomenon (see M.J. Rees’s review in this volume). By examining the recent observational information from Ariel V, HEAO-1, and the Einstein Observatory, we have reached the conclusion (Tsuruta 1981) that the following interpretation may be used as a relevant ...
S. Tsuruta, F. Takahara, S. Ichimaru
openaire   +1 more source

The X-Ray Spectra of Active Galactic Nuclei

Physica Scripta, 1984
Recent 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.
openaire   +1 more source

X-Ray Timing and Spectral Observations of Active Galactic Nuclei

Space Science Reviews, 1985
Over 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 ...
openaire   +1 more source

X-Ray Variability in Active Galactic Nuclei

1998
X-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.
openaire   +1 more source

The X-ray variability of active galactic nuclei

2008
Recent 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.
openaire   +1 more source

X-Ray Spectra of Active Galactic Nuclei

1980
There 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 ...
openaire   +1 more source

An Explanation for the Soft X-Ray Excess in Active Galactic Nuclei

2007
We present a large sample of type 1 active galactic nuclei (AGN) spectra taken with XMM‐ Newton, and fit them with both the conventional model (a power law and blackbody) and the relativistically blurred photoionized disc reflection model of Ross & Fabian. We find that the disc reflection model is a better fit.
Crummy, J., Fabian, A., Gallo, L., Ross, R.   +3 more
openaire   +3 more sources

The soft X-ray spectra of active galactic nuclei

2008
EXOSAT 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).
openaire   +1 more source