scholarly journals The Shape of Soft X-ray Spectra of Quasars

1989 ◽  
Vol 134 ◽  
pp. 175-176
Author(s):  
D. A. Schwartz ◽  
Y. Qian ◽  
W. H. Tucker
Keyword(s):  
Flux Density ◽  
Power Laws ◽  
Seyfert Galaxies ◽  
Background Spectrum ◽  
X Ray ◽  
The Mean ◽  
X Ray Background ◽  
Image Position ◽  
Two Parameters ◽  
Lines Of Evidence

Several lines of evidence suggest that the x-ray spectra of quasars are not simple, exact power laws: 1. when Wilkes and Elvis (1987) analyzed quasars as power laws they found an absorption less than that due to our galaxy; 2. The mean 0.3 to 3.5 keV spectral index is steeper than the mean for the 2 to 20 keV range; 3. although several lines of evidence argue that AGN provide a significant portion (perhaps all) of the x-ray background, the diffuse background spectrum does not agree with the x-ray power-law indices measured for quasars or Seyfert galaxies. Schwartz and Tucker (1988) have suggested that all the above conflicts are reconciled if the slope in the Log(flux density) vs. Log(energy) plot flattens continuously with increasing energy. In this paper we utilize one particular parameterization suggested for the flux density, which we call the “log-slope” model: where f is the flux density, K a normalization parameter which is not of interest here, and a and b are the two parameters of our fit.

scholarly journals The Sources of the Hard X-Ray Background

1996 ◽  
Vol 168 ◽  
pp. 263-270
Author(s):  
Giancarlo Setti ◽  
Andrea Comastri
Keyword(s):  
Energy Spectrum ◽  
Energy Density ◽  
Energy Flux ◽  
Large Fraction ◽  
Power Laws ◽  
Prima Facie ◽  
Folding Energy ◽  
Hard Component ◽  
X Ray ◽  
X Ray Background

The hard component (3 keV – ~ MeV) of the X-ray background (XRB) comprises the largest portion, ~ 90%, of the overall XRB intensity. The observed isotropy (the entire Galaxy is transparent above 3 keV) provides aprima facieevidence of its prevailing extragalactic nature. A large fraction (~ 75%) of the energy flux falls in the 3 – 100 keV band, the corresponding energy density being ≃ 5×10−5eV cm−3, of which 50% is confined to the narrower 3 – 20 keV band. Although the energy flux carried by the XRB is relatively small compared to other extragalactic backgrounds, it was soon realized that it cannot be accounted for in terms of sources and processes confined to the present epoch. An analysis of the combined observed spectra (Gruber 1992) concludes that, while a thermal bremsstrahlung with an e-folding energy = 41.13 keV accurately fits the data up to 60 keV, above this energy the sum of two power laws is required with normalizations such that at 60 keV the spectral index is ~ 1.6, gradually flattening to ~ 0.7 at MeV energies. It should also be noted that below 10 keV the XRB energy spectrum is well represented by a power law of index α = 0.4 (I∝E−α).

scholarly journals X-ray Constraints on AGN Clustering

1989 ◽  
Vol 134 ◽  
pp. 492-493
Author(s):  
G. De Zotti ◽  
M. Persic ◽  
A. Franceschini ◽  
L. Danese ◽  
G.G.C. Palumbo ◽  
...  
Keyword(s):  
Space Distribution ◽  
Background Intensity ◽  
Additional Contribution ◽  
List Type ◽  
X Ray ◽  
Upper Limit ◽  
Angular Scale ◽  
Sky Survey ◽  
The Mean ◽  
X Ray Background

Studies of the HEAO–1 A2 all–sky survey data have established that the level of anisotropy of the extragalactic X–ray background (XRB) is relatively low: –The cell–to–cell XRB intensity variations can be entirely accounted for by Poisson fluctuations in the space distribution of known classes of sources; the 90% confidence upper limit to any additional contribution on a scale of 26 square degrees is 2.3% (Shafer and Fabian 1983).–No significant correlations of XRB intensity fluctuations appear to be present; the formal 90% confidence upper limit on the amplitude of autocorrelations, relative to the mean background intensity, for an angular scale of 3° is Γ(3°) ≤ 1.9 × 10−2 (Persic et al. 1988).

An Improved Mean Atomic Number Background Correction for Quantitative Microanalysis

1996 ◽  
Vol 2 (1) ◽  
pp. 1-7 ◽  
Author(s):  
John J. Donovan ◽  
Tracy N. Tingle
Keyword(s):  
Atomic Number ◽  
Minor Element ◽  
Binary Compound ◽  
Primary Electron ◽  
Background Correction ◽  
X Ray ◽  
The Mean ◽  
Set Up ◽  
X Ray Background ◽  
The Continuum

Quantitative EPMA (electron probe microanalysis) intensity measurements require an accurate correction for the X-ray continuum (or background) created by the Bremsstrahlung effect from the primary electron beam. This X-ray continuum, as measured on a wavelength-dispersive spectrometer at any particular wavelength, is primarily a function of the mean atomic number of the material being analyzed. One can calibrate the dependence of the continuum on mean atomic number by measuring and curve fitting the X-ray intensities at the analytical peak in pure elements, oxides, and binary compound standards that do not contain any of the analyte or any interfering elements and use that calibration to calculate the X-ray background correction. For unknown samples, the mean atomic number is determined from the elemental concentrations calculated by the ZAF or φ(ρz) matrix correction, and the fit regression coefficients are used iteratively to calculate the actual background correction. Over a large range of mean atomic number we find that the dependence of the continuum intensity on mean atomic number is well described by a second-order polynomial fit. In the case of low-energy X-ray lines (<1 to 2 keV), this fit is significantly improved by correcting the X-ray continuum intensities for absorption. For major and most minor element analyses, the improved mean atomic number background correction procedure presented in this paper is accurate and robust for a wide variety of samples. Empirical mean atomic number background data are presented for a typical 10-element silicate and a 15-element sulfide analytical set up that demonstrate the validity of the technique as well as some potential limitations.

The 20keV Break in the Diffuse X-ray Background Spectrum

1977 ◽  
Vol 3 (2) ◽  
pp. 131-132
Author(s):  
R. M. Hudson ◽  
R. M. Thomas ◽  
M. L. Duldig
Keyword(s):  
Spectral Index ◽  
Simple Analysis ◽  
Background Spectrum ◽  
X Ray ◽  
Independent Determination ◽  
Analysis Technique ◽  
X Ray Background

In this paper we report an independent determination of the Location of the break (change in spectral index) in the spectrum of the diffuse X-ray background by applying a simple analysis technique to data already in the literature.

scholarly journals The Soft X-ray Background Spectrum from DXS

1997 ◽  
Vol 166 ◽  
pp. 83-90 ◽  
Author(s):  
W.T. Sanders ◽  
R.J. Edgar ◽  
D.A. Liedahl ◽  
J.P. Morgenthaler
Keyword(s):  
Galactic Plane ◽  
Emission Lines ◽  
Background Spectrum ◽  
Local Bubble ◽  
X Ray ◽  
Hot Plasma ◽  
Solar Abundances ◽  
Ionic Emission ◽  
X Ray Background ◽  
Ionization Balance

AbstractThe Diffuse X-ray Spectrometer (DXS) obtained spectra of the low energy X-ray (44 – 83 Å) diffuse background near the galactic plane from galactic longitudes 150° ≲ l ≲ 300° with ≲ 3 Å spectral resolution and ~ 15° angular resolution. Thus, DXS measured X-ray spectra that arise almost entirely from within the Local Bubble. The DXS spectra show emission lines and emission-line blends, indicating that the source of the X-ray emission is thermal – hot plasma in the Local Bubble. The measured spectra are not consistent with those predicted by standard coronal models, either with solar abundances or depleted abundances, over the temperature range 105 – 107 K. The measured spectra are also inconsistent with the predictions of various non-equilibrium models. A nearly acceptable fit to DXS spectra can be achieved using a hybrid model that combines the Raymond & Smith ionization balance calculation with recently calculated (by DAL) ionic emission lines.

scholarly journals Seyfert Galaxies and the Hard X-Ray Background: ArtificialChandraObservations of [FORMULA][F]z=0.3[/F][/FORMULA] Active Galaxies

2006 ◽  
Vol 131 (1) ◽  
pp. 133-142 ◽  
Author(s):  
K. C. Peterson ◽  
S. C. Gallagher ◽  
A. E. Hornschemeier ◽  
M. P. Muno ◽  
E. C. Bullard
Keyword(s):  
Seyfert Galaxies ◽  
Active Galaxies ◽  
X Ray ◽  
X Ray Background
Sign in / Sign up

Export Citation Format

Share Document