1,322 research outputs found

    The X-ray spectrum and time variability of narrow emission line galaxies

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    X-ray spectral and temporal observations are reported for six narrow emission line galaxies (NELGs), all of which are fitted by power-law X-ray spectra of energy slope 0.8 and have column densities in the line of sight greater than 1 x 10 to the 22nd atoms/sq cm. Three of the objects, NGC 526a, NGC 2110 and MCG-5-23-16 are variable in their X-ray flux, and the latter two, along with NGC 5506 and NGC 7582, showed detectable variability in at least one observation. The measured X-ray properties of these NELGs, which also included NGC 2992, strongly resemble those of previously-measured type 1 Seyferts of the same X-ray luminosity and lead to the conclusion of great similarity between the NELGs and low-luminosity type 1 Seyferts. The implications of these observations for the optical line-emitting region structure of these galaxies are discussed

    X-ray emission from active galactic nuclei

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    It is often held that the X-ray emission from active galactic nuclei (AGN) arises from a region close to the central energy source. Thus X-ray observations may provide the best constraints on the central engine. In particular, the shape of the X-ray continuum gives information about the mechanism for photon generation, X-ray time variability data can constrain the size and mass of the continuum source, and X-ray occultation data give constraints on the relative sizes of the continuum source and the intervening absorbing material (often assumed to be the broad line clouds). In addition, since a fair fraction of the total energy of an AGN is emitted at X-ray wavelengths, direct measurement of the amount and spectral form of this radiation is important for modeling of the optically emitting clouds

    X-ray spectra of clusters of galaxies

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    The X-ray emission from luminous clusters of galaxies is dominated by thermal bremsstrahlung from an intergalactic medium. The central density of the gas is strongly correlated with the X-ray surface brightness. The X-ray surface brightness S(sigma) of many clusters is well modeled by a law of the form S(sigma) alpha S(o) 1 + R(2)/A(2) to the minus 3 beta + 1/2 power with beta approximately equal to 0.66. However, this model does not fit the X-ray spectral or optical galaxy counts well. In clusters with cooling flows in their center there is a strong correlation between the cooling rates of X-ray emitting material and optical H alpha emission. It is not clear, at present, what percentage of the virial mass of the cluster is in hot gas but if beta = 0.66, it is possible for the values to be of the order of 1/2. Spatially resoled X-ray spectroscopy is necessary to determine this value with any accuracy

    X-ray spectra and time variability of active galactic nuclei

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    The X-ray spectra of broad line active galactic nuclei (AGN) of all types (Seyfert I's, NELG's, broadline radio galaxies) are well fit by a power law in the .5 to 100 keV band of man energy slope alpha = .68 + or - .15. There is, as yet, no strong evidence for time variability of this slope in a given object. The constraints that this places on simple models of the central energy source are discussed. BL Lac objects have quite different X-ray spectral properties and show pronounced X-ray spectral variability. On time scales longer than 12 hours most radio quiet AGN do not show strong, delta I/I .5, variability. The probability of variability of these AGN seems to be inversely related to their luminosity. However characteristics timescales for variability have not been measured for many objects. This general lack of variability may imply that most AGN are well below the Eddington limit. Radio bright AGN tend to be more variable than radio quiet AGN on long, tau approx 6 month, timescales

    X-ray emission from clusters of galaxies

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    Some X-ray spectral observations of approximately 30 clusters of galaxies from HEAO-1 are summarized. There exists strong correlations between X-ray luminosity, L(x), and temperature kT in the form L(x)alphaT to the 2.3 power. This result combined with the L(x) central galaxy density relation and the virial theorem indicates that the core dadius of the gas should be roughly independent of L(x) or KT and that more luminous clusters have a greater fraction of their virial mass in gas. The poor correlation of KT and optical velocity dispersion seems to indicate that clusters have a variety of equations of state. There is poor agreement between X-ray imaging observations and optical and X-ray spectral measures of the polytropic index. Most clusters show Fe emission lines with a strong indication that they all have roughly 1/2 solar abundance. The evidence for cooling in the cores of several clusters is discussed based on spectral observations with the Einstein solid state spectrometer

    The line continuum luminosity ratio in AGN: Or on the Baldwin Effect

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    The luminosity dependence of the equivalent width of CIV in active galaxies, the "Baldwin" effect, is shown to be a consequence of a luminosity dependent ionization parameter. This law also agrees with the lack of a "Baldwin" effect in Ly alpha or other hydrogen lines. A fit to the available data gives a weak indication that the mean covering factor decreases with increasing luminosity, consistent with the inference from X-ray observations. The effects of continuum shape and density on various line ratios of interest are discussed
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