<i>Chandra</i>Survey of Radio‐quiet, High‐Redshift Quasars

Bechtold, Jill; Siemiginowska, Aneta; Shields, J. C.; Czerny, B.; Janiuk, Agnieszka; Hamann, Fred; Aldcroft, Thomas L.; Elvis, M.; Dobrzycki, A.

doi:10.1086/378724

Cited by 80 publications

(133 citation statements)

References 85 publications

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“…A strong correlation between ox a and the optical luminosity at 2500 Å is found, while ox a is only marginally dependent upon redshift (but see Bechtold et al 2003 for different results). The ox a distributions typically cover the range 1.2, 1.8, with a mean value of about 1.5.…”

Section: Introductionmentioning

confidence: 90%

The Tight Relation Between X-Ray and Ultraviolet Luminosity of Quasars

Lusso

Risaliti

2016

ApJ

246

323

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The observed relation between the soft X-ray and the optical-ultraviolet emission in active galactic nuclei (AGNs) is nonlinear and it is usually parametrized as a dependence between the logarithm of the monochromatic luminosity at 2500 Å and at 2 keV. Previous investigations have found that the dispersion of this relation is rather high (∼0.35-0.4 in log units), which may be caused by measurement uncertainties, variability, and intrinsic dispersion due to differences in the AGN physical properties (e.g., different accretion modes). We show that, once optically selected quasars with homogeneous SED and X-ray detection are selected, and dust reddened and/or gas obscured objects are not included, the measured dispersion drops to significantly lower values (i.e., ∼0.21-0.24 dex). We show that the residual dispersion is due to some extent to variability, and to remaining measurement uncertainties. Therefore, the real physical intrinsic dispersion should be 0.21 < dex. Such a tight relation, valid over four decades in luminosity, must be the manifestation of an intrinsic (and universal) physical relation between the disk, emitting the primary radiation, and the hot electron corona emitting X-rays.

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Section: Introductionmentioning

confidence: 90%

The Tight Relation Between X-Ray and Ultraviolet Luminosity of Quasars

Lusso

Risaliti

2016

ApJ

246

323

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“…This differs from Paper I in that we do not use the measured L 5100 Å , which is potentially affected by galaxy starlight. In Figure 3, we plot α ox versus the monochromatic luminosity at 2500 Å, a well known correlation (Avni & Tananbaum 1982;Bechtold et al 2003). We include the X-ray-weak NLS1 sample of Williams et al (2004), X-ray-selected NLS1s (Grupe et al 2004), and the PG quasars that are classified as NLS1s according to FWHM Hβ (Boroson & Green 1992), with α ox given by Brandt et al (2000).…”

Section: X-ray-to-optical Flux Ratiomentioning

confidence: 99%

X-Ray Properties of Intermediate-Mass Black Holes in Active Galaxies. Ii. X-Ray-Bright Accretion and Possible Evidence for Slim Disks

Desroches

Greene

2009

ApJ

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We present X-ray properties of optically selected intermediate-mass (∼10 5 -10 6 M ) black holes (BHs) in active galactic nuclei (AGNs), using data from the Chandra X-Ray Observatory. Our observations are a continuation of a pilot study by Greene & Ho. Of the eight objects observed, five are detected with X-ray luminosities in the range L 0.5-2 keV = 10 41 -10 43 erg s −1 , consistent with the previously observed sample. Objects with enough counts to extract a spectrum are well fit by an absorbed power law. We continue to find a range of soft photon indices 1 < Γ s < 2.7, where N (E) ∝ E −Γ s , consistent with previous AGN studies, but generally flatter than other narrow-line Seyfert 1 active nuclei (NLS1s). The soft photon index correlates strongly with X-ray luminosity and Eddington ratio, but does not depend on BH mass. There is no justification for the inclusion of any additional components, such as a soft excess, although this may be a function of the relative inefficiency of detecting counts above 2 keV in these relatively shallow observations. As a whole, the X-ray-to-optical spectral slope α ox is flatter than in more massive systems, even other NLS1s. Only X-ray-selected NLS1s with very high Eddington ratios share a similar α ox . This is suggestive of a physical change in the accretion structure at low masses and at very high accretion rates, possibly due to the onset of slim disks. Although the detailed physical explanation for the X-ray loudness of these intermediate-mass BHs is not certain, it is very striking that targets selected on the basis of optical properties should be so distinctly offset in their broader spectral energy distributions.

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“…The X-ray to optical flux ratio distribution of an X-ray selected sample of 188 type 1 AGN from the ChaMP survey, which is limited to bright X-ray fluxes and optical luminosities ( f x > 10 14 erg cm −2 s −1 and r < 22.5), is presented in Silverman et al (2005). A strong correlation between α ox and the optical luminosity at 2500 Å is found, while α ox is only marginally dependent upon redshift (but see Bechtold et al 2003, for different results). The α ox distributions typically cover the range 1.2−1.8, with a mean value of about 1.5.…”

Section: Introductionmentioning

confidence: 96%

The X-ray to optical-UV luminosity ratio of X-ray selected type 1 AGN in XMM-COSMOS

Lusso

Comastri

Vignali

et al. 2010

A&A

359

284

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We present a study of the X-ray to optical properties of a sample of 545 X-ray selected type 1 AGN, from the XMM-COSMOS survey, over a wide range of redshifts (0.04 < z < 4.25) and X-ray luminosities (40.6 ≤ Log L [2−10] keV ≤ 45.3). About 60% of them are spectroscopically identified type 1 AGN, while the others have a reliable photometric redshift and are classified as type 1 AGN on the basis of their multi-band Spectral Energy Distributions. We discuss the relationship between UV and X-ray luminosity, as parameterized by the α ox spectral slope, and its dependence on redshift and luminosity. We compare our findings with previous investigations of optically selected broad-line AGN (mostly from SDSS). A highly significant correlation between α ox and L 2500 Å is found, in agreement with previous investigations of optically selected samples. We calculate bolometric corrections, k bol , for the whole sample using hard X-ray luminosities (L [2−10] keV ), and the Eddington ratios for a subsample of 150 objects for which black hole mass estimates are available. We confirm the trend of increasing bolometric correction with increasing Eddington ratio as proposed in previous works. A tight correlation is found between α ox and k bol , which can be used to estimate accurate bolometric corrections using only optical and X-ray data. We find a significant correlation between α ox and Eddington ratio, in which the ratio between X-ray and optical flux decreases with increasing Eddington ratio.

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ChandraSurvey of Radio‐quiet, High‐Redshift Quasars

Cited by 80 publications

References 85 publications

The Tight Relation Between X-Ray and Ultraviolet Luminosity of Quasars

The Tight Relation Between X-Ray and Ultraviolet Luminosity of Quasars

X-Ray Properties of Intermediate-Mass Black Holes in Active Galaxies. Ii. X-Ray-Bright Accretion and Possible Evidence for Slim Disks

The X-ray to optical-UV luminosity ratio of X-ray selected type 1 AGN in XMM-COSMOS

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