Diagnosis: Philosophical and Medical Perspectives

Laor, Nathaniel; Agassi, Joseph

doi:10.1007/978-94-009-2085-9

Cited by 74 publications

(80 citation statements)

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“…7 and 8, though the accretion rates in units of the Eddington accretion rates for PG quasars are consistent with the results of Laor (1990), we can see that accretion rates in units of the Eddington accretion rates of most of the Seyfert 1 galaxies are larger than one. We confirmed the results of Collin & Hure (2001).…”

Section: Discussionsupporting

confidence: 88%

Masses, accretion rates and inclinations of AGNs

Bian

Zhao

2002

A&A

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Abstract. We assume that the gravitational instability of standard thin accretion disks leads to the Broad Line Regions (BLRs), the B band luminosity comes from standard thin disk and the motion of BLRs is virial. The central black hole masses, the accretion rates and the disk inclinations to the line of sight for 17 Seyfert 1 galaxies and 17 Palomar-Green (PG) quasars have been calculated. Our results are sensitive to the α parameter of the standard α disk. With the same values of α (α = 1), calculated central black hole masses for 17 Seyfert 1 galaxies are consistent with those from Kaspi et al. (2000) while those for 17 PG quasars are larger than those from Kaspi et al. (2000) by almost 2 orders of magnitude. Inclinations of 17 Seyfert 1 galaxies are about 6 times larger than those of 17 PG quasars. These inclinations, with a mean value of 32• for 17 Seyfert 1 galaxies that agrees well with the result obtained by fitting the iron Kα lines of Seyfert 1 galaxies observed with ASCA (Nandra et al. 1997) and the result obtained by Wu & Han (2001), provide further support for the orientation-dependent unification scheme of active galactic nuclei. There is a relation between the FWHM of Hβ and the inclination, namely the inclination is smaller in AGNs with smaller FWHM of Hβ. The effect of inclinations in narrow line Seyfert 1 galaxies (NLS1s) should be considered when one studies the physics of NLS1s. The need for higher value of α for PG quasars maybe shows that our model is not suitable for PG quasars if we think inclinations of PG quasars are in the inclination levels of Seyfert 1 galaxies. With our model, we also show that the size of BLRs relates not only to the luminosity, but also to the accretion rates. More knowledge of BLR dynamics, accretion disks and optical luminosity are needed to improve the determination of black hole masses, accretion rates and inclinations in AGNs.

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Section: Discussionsupporting

confidence: 88%

Masses, accretion rates and inclinations of AGNs

Bian

Zhao

2002

A&A

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“…This so-called big blue bump is thus often identified with the putative AD. The observed quasar continuum from the FUV to the NIR is broadly consistent with the predictions from the standard model (e.g., Malkan 1983;Czerny & Elvis 1987;Laor 1990;Pereyra et al 2006;Kishimoto et al 2008).…”

Section: Quasar Continuum From the Extreme Uv To The Near-irsupporting

confidence: 83%

Ultraviolet variability of quasars: dependence on the accretion rate

Meusinger

Weiss

2013

A&A

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Aims. Although the variability in the ultraviolet and optical domain is one of the major characteristics of quasars, the dominant underlying mechanisms are still poorly understood. There is a broad consensus on the relationship between the strength of the variability and such quantities as time-lag, wavelength, luminosity, and redshift. However, evidence on a dependence on the fundamental parameters of the accretion process is still inconclusive. This paper is focused on the correlation between the ultraviolet quasar long-term variability and the accretion rate. Methods. We compiled a catalogue of about 4000 quasars including individual estimators for the variability strength derived from the multi-epoch photometry in the SDSS Stripe 82, virial black hole masses M derived from the Mg  line, and mass accretion ratesṀ from the Davis-Laor scaling relation. Several statistical tests were applied to evaluate the correlations of the variability with luminosity, mass, Eddington ratio, and accretion rate. Results. We confirm the existence of significant anti-correlations between the variability estimator V and the accretion rateṀ, the Eddington ratio ε, and the bolometric luminosity L bol , respectively. The Eddington ratio is tightly correlated withṀ. A weak, statistically not significant positive trend is indicated for the dependence of V on M. As a side product, we find a strong correlation of the radiative efficiency η with M in our sample. We show via numerical simulations that this trend is most likely produced by selection effects in combination with the mass errors and the use of the scaling relation forṀ. The anti-correlations of V withṀ, ε, and L bol cannot be explained in such a way. The strongest anti-correlation is found between V andṀ. However, it is difficult to decide which of the quantities L, ε, andṀ is intrinsically correlated with V and which of the observed correlations of V are produced by the L − ε −Ṁ relation. A V −Ṁ anti-correlation is qualitatively expected for the strongly inhomogeneous accretion disks. We argue that the observed amplitudes of the variability at far-UV wavelengths, the stochastic nature of variability, and the variability time-scales are not adequately explained by the simple multi-temperature black-body model of a standard disk and suggest to check whether the strongly inhomogeneous disk model is capable of reproducing these observations better.

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“…Laor 1990). Evidences of this thermal component have been found in other quasartype blazars, such as 3C 273 (Smith et al 1993;von Montigny et al 1997;Grandi & Palumbo 2004;Türler et al 2006), 3C 279 (Pian et al 1999), and 3C 345 (Bregman et al 1986).…”

Section: Results From Ommentioning

confidence: 99%

WEBT and XMM-Newton observations of 3C 454.3 during the post-outburst phase

Raiteri¹,

Villata²,

Larionov

et al. 2007

A&A

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Context. The quasar-type blazar 3C 454.3 was observed to undergo an unprecedented optical outburst in spring 2005, affecting the source brightness from the near-IR to the X-ray frequencies. This was first followed by a millimetric and then by a radio outburst, which peaked in February 2006. Aims. In this paper we report on follow-up observations to study the multiwavelength emission in the post-outburst phase. Results. The source was in a faint state. The radio flux at the higher frequencies showed a fast decreasing trend, which represents the tail of the big radio outburst. It was followed by a quiescent state, common at all radio frequencies. In contrast, moderate activity characterized the near-IR and optical light curves, with a progressive increase of the variability amplitude with increasing wavelength. We ascribe this redder-when-brighter behaviour to the presence of a "little blue bump" due to line emission from the broad line region, which is clearly visible in the source spectral energy distribution (SED) during faint states. Moreover, the data from the XMM-Newton Optical Monitor reveal a rise of the SED in the ultraviolet, suggesting the existence of a "big blue bump" due to thermal emission from the accretion disc. The X-ray spectra are well fitted with a power-law model with photoelectric absorption, possibly larger than the Galactic one. However, the comparison with previous X-ray observations would imply that the amount of absorbing matter is variable. Alternatively, the intrinsic X-ray spectrum presents a curvature, which may depend on the X-ray brightness. In this case, two scenarios are possible. i) There is no extra absorption, and the X-ray spectrum hardens at low energies, the hardening being more evident in bright states; ii) there is a constant amount of extra absorption, likely in the quasar environment, and the X-ray spectrum softens at low energies, at least in faint X-ray states. This softening might be the result of a flux contribution by the high-frequency tail of the big blue bump.

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Diagnosis: Philosophical and Medical Perspectives

Cited by 74 publications

References 0 publications

Masses, accretion rates and inclinations of AGNs

Masses, accretion rates and inclinations of AGNs

Ultraviolet variability of quasars: dependence on the accretion rate

WEBT and XMM-Newton observations of 3C 454.3 during the post-outburst phase

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