X-ray studies of quasars with the Einstein Observatory

Tananbaum, H.; Avni, Y.; Branduardi, G.; Elvis, M.; Fabbiano, G.; Feigelson, E.; Giacconi, R.; Henry, J. P.; Pye, J. P.; Sołtan, A.; Zamorani, G.

doi:10.1086/183100

Cited by 417 publications

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“…Such preference was principally due to historical reasons: the first analyses back in the early 1980s were carried out with data where these monochromatic values were easy to measure (Tananbaum et al 1979;Zamorani et al 1981;Avni & Tananbaum 1986). Largely used even nowadays (principally for the sake of comparison with previous works), such endpoints at 2500 Å and 2 keV are still observationally convenient.…”

Section: The Choice Of Observablesmentioning

confidence: 99%

“…An important observational result concerning the link between the BBB (disc) and X-ray emission (corona) is provided by the non-linear correlation between the monochromatic optical luminosity at 2500 Å (L UV ) and the one in the X-rays at 2 keV (L X , Tananbaum et al 1979;Zamorani et al 1981;Avni & Tananbaum 1986). The non-linear relationship between L X and L UV (parameterised as log L X = γ log L UV + β) has been found in both optically and X-ray selected AGN samples and exhibits a slope γ around 0.5 − 0.7 (Vignali et al 2003;Strateva et al 2005;Steffen et al 2006;Just et al 2007;Green et al 2009;Lusso et al 2010;Young et al 2010;Marchese et al 2012;Jin et al 2012), implying that optically bright AGN emit relatively less X-rays than optically faint AGN.…”

Section: Introductionmentioning

confidence: 99%

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Quasars as standard candles

Lusso

Risaliti

2017

A&A

138

107

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Context. A tight non-linear relation exists between the X-ray and UV emission in quasars (i.e. L X ∝ L γ UV ), with a dispersion of ∼0.2 dex over approximately three orders of magnitude in luminosity. Such observational evidence has two relevant consequences:(1) an ubiquitous physical mechanism must regulate the energy transfer from the accretion disc to the X-ray emitting corona, and (2) the non-linearity of the relation provides a new, powerful way to estimate the absolute luminosity, turning quasars into a new class of standard candles. Aims. Here we propose a modified version of this relation, which involves the emission line full-width half maximum, L X ∝ Lˆγ UV υˆβ fwhm . Methods. We interpret this new relation through a simple, ad-hoc model of accretion disc corona, derived from previous works in the literature where it is assumed that reconnection and magnetic loops above the accretion disc can account for the production of the primary X-ray radiation. Results. We find that the monochromatic optical-UV (2500 Å) and X-ray (2 keV) luminosities depend on the black hole mass and accretion rate as L UV ∝ M 4/3 BH (Ṁ/Ṁ Edd ) 2/3 and L X ∝ M 19/21 BH (Ṁ/Ṁ Edd ) 5/21 , respectively. Assuming a broad line region size function of the disc luminosity R blr ∝ L 0.5 disc we finally have that L X ∝ L 4/7 UV υ 4/7 fwhm . Such relation is remarkably consistent with the slopes and the normalisation obtained from a fit of a sample of 545 optically selected quasars from SDSS DR7 cross matched with the latest XMM-Newton catalogue 3XMM-DR6. Conclusions. The homogeneous sample used here has a dispersion of 0.21 dex, which is much lower than previous works in the literature and suggests a tight physical relation between the accretion disc and the X-ray emitting corona. We also obtained a possible physical interpretation of the L X − L UV relation (considering also the effect of υ fwhm ), which puts the determination of distances based on this relation on a sounder physical grounds. The proposed new relation does not evolve with time, and thus it can be employed as a cosmological indicator to robustly estimate cosmological parameters.

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Section: The Choice Of Observablesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quasars as standard candles

Lusso

Risaliti

2017

A&A

138

107

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“…To characterize this ratio, we use α ox , the slope of a hypothetical power law extending from 2500 Å to 2 keV (Tananbaum et al 1979). We adopt the following definition: α ox ≡ −0.3838 log(f 2500 Å /f 2 keV ) (Strateva et al 2005).…”

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 radio fluxes at 1.4 GHz are taken from the NRAO VLA Sky Survey (NVSS, Condon et al 1998). The twopoint spectral indices α ox = −log(S 2keV /S 2500Å )/2.605 and α ro = log(S 5 GHz /S 2500Å )/5.38 (Stocke et al 1985;Tananbaum et al 1979) have been K-corrected for the redshift of the object by assuming spectral slopes within each band of α r = −0.7; α x = −1 and α o = −1.4 (Ghisellini et al 1986). X-ray photon index for a power law fit with Galactic absorption.…”

Section: Criteria For Classificationmentioning

confidence: 99%

An AGN sample with high X-ray-to-optical flux ratio from RASS

Wei

Dong

et al. 1999

Astron. Astrophys. Suppl. Ser.

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Abstract. We present the first results of a program to identify the unknown bright active galactic nuclei (AGN) in the ROSAT All Sky Survey Bright Source Catalog (RASS-BSC). We have used log C + 0.4 R as an alternative expression for log(f X /f opt ), where C is X-ray count rate and R stands for R magnitude. Then a high X-rayto-optical flux ratio criterion has been used to select an AGN sample with 165 unidentified X-ray sources for optical spectroscopy. Those 165 X-ray sources have been identified in the following classes: 115 emission line AGN (QSOs and Seyferts), 2 BL Lac objects and 4 BL Lac candidates, 22 clusters of galaxies, 12 Galactic stars and 10 objects remain unidentified. This represent a success rate of about 73% for detecting AGN using our selection criteria. Plausibility is based upon the optical classification and X-ray characteristics of the sources.

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X-ray studies of quasars with the Einstein Observatory

Cited by 417 publications

References 0 publications

Quasars as standard candles

Quasars as standard candles

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

An AGN sample with high X-ray-to-optical flux ratio from RASS

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