Two-phase models of quasar emission line regions

Krolik, Julian H.; McKee, Christopher F.; Tarter, C. Bruce

doi:10.1086/159303

Cited by 480 publications

(505 citation statements)

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“…Illumination of a disk by hard X-rays leads to the formation of a very hot, optically thin layer of material above the disk (Krolik et al 1981). In the hot layer, Comptonization and bremstrahlung play the main roles, but closer to the cool, dense disc, atomic absorption and emission become the major cooling processes.…”

Section: Discussionmentioning

confidence: 99%

XMM–Newtonobservations of the Seyfert 1 galaxy ESO 141–G55

Gondoin

Orr

Lumb

2003

A&A

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Abstract.We report on an observation of the Seyfert 1 galaxy ESO 141-G55 performed in October 2001 with the EPIC MOS cameras and Reflection Grating Spectrometers (RGS) on board the XMM-Newton observatory. We find the hard (3-10 keV) continuum slope, including reflection, to be somewhat flatter (Γ = 1.72 ± 0.06) than that of a typical broad-line Seyfert 1 galaxy. The spectrum shows a weak emission line at 6.45 ± 0.04 keV with a measured equivalent width of ≈40 eV. A broad spectral feature is observed around 7 keV that can be fitted by an absorption edge at 7.6 ± 0.1 keV. The extrapolation of the primary power law continuum to energies lower than 2 keV indicates the presence of a soft excess component contributing to 45 ± 3% of the overall flux in the 0.3−2.0 keV energy range. This soft-excess cannot be explained solely by enhanced reflection from a highly ionized disk.

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Section: Discussionmentioning

confidence: 99%

XMM–Newtonobservations of the Seyfert 1 galaxy ESO 141–G55

Gondoin

Orr

Lumb

2003

A&A

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“…As discussed in Krolik, Mckee, & Tarter (1981) and, more recently, in Krolik & Kriss (2001), there are two regimes of ionization (characterized by the '' pressure '' ionization parameter, or U=T) and temperature wherein a cloud of photoionized gas is stable to thermal perturbations: at low ionization/temperature, when line cooling is efficient, and at high temperature/ionization, when thermal balance is achieved via Compton processes. In the intermediate region, small changes in ionization can result in large changes in temperature.…”

Section: The Nature Of the Outflowmentioning

confidence: 99%

Variable Ultraviolet Absorption in the Seyfert 1 Galaxy NGC 3516: The Case for Associated Ultraviolet and X‐Ray Absorption

Kraemer

Crenshaw

George

et al. 2002

ApJ

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We present observations of the UV absorption lines in the Seyfert 1 galaxy NGC 3516, obtained at a resolution of =D % 40; 000 with the Space Telescope Imaging Spectrograph (STIS) on 2000 October 1. The UV continuum was $4 times lower than that observed during 1995 with the Goddard High Resolution Spectrograph (GHRS), and the X-ray flux from a contemporaneous Chandra X-Ray Observatory observation was a factor of $8 below that observed with ASCA. The STIS spectra show kinematic components of absorption in Ly , C iv, and N v at radial velocities of À376, À183, and À36 km s À1 (components 1, 2, and 3+4, respectively), which were detected in the earlier GHRS spectra; the last of these is a blend of two GHRS components that have increased greatly in column density. Four additional absorption components have appeared in the STIS spectra at radial velocities of À692, À837, À994, and À1372 km s À1 (components 5-8); these may also have been present in earlier low-flux states observed by the International Ultraviolet Explorer. Based on photoionization models, we suggest that the components are arranged in increasing radial distance in the order 3+4, 2, 1, followed by components 5-8. We have achieved an acceptable fit to the X-ray data using the combined X-ray opacity of the UV components 1, 2, and 3+4. By increasing the UV and X-ray fluxes of these models to match the previous high states, we are able to match the GHRS C iv column densities, the absence of detectable C iv absorption in components 5-8, and the 1994 ASCA spectrum. We conclude that variability of the UV and X-ray absorption in NGC 3516 is primarily due to changes in the ionizing flux.

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“…The physical conditions indicated in Table I are free parameters, but we require them to have the values shown in order to fit the models to the data. On the other hand, the existence and physical state of gas, at least in the BLR, may actually be predictable from physical principles, at least in the widely accepted theory of Krolik, McKee, and Tarter (1981). We may ask what will be the physical state of gas being heated by a continuum such as the one observed?…”

Section: Orthodox Classification Of Active Galactic Nucleimentioning

confidence: 99%

“…Swimming against the tide, one set of authors (Guilbert, Fabian, and McCray 1983) have produced a model which does not involve amplification but does involve a BL Lac phase for AGN in which gas is not available for ionization. The idea is based on the work of Krolik et al (1981) which explains the formation of BLR clouds in gas heated by photoionization (see Section II).…”

Section: Continuum Vs Lines-the Bl Lac Phenomenonmentioning

confidence: 99%

Classification of active galaxies and the prospect of a unified phenomenology

Lawrence

1987

PASP

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The observational classification of active galaxies is reviewed and its likely meaning discussed. A large number of facts and ideas are examined, but a particular set of ideas is stressed as our best hope for a unified phenomenology, as follows. There is only one kind of Active Galactic Nucleus (AGN). The observed variety arises from three degrees of freedom: (1) Dust opacity, which produces the distinction between Type 1 and Type 2 AGN. (2) Viewing angle of a relativistic jet, which produces the distinction between blazars and Type 1 AGN. (3) Duty cycle of activity (i.e., fraction of time spent "on") which produces the distinction between radio-loud and radio-quiet AGN. The duty cycle may be related to the mass of the spheroidal component of the parent galaxy. A fourth degree of freedom is, of course, the overall luminosity. Also, it has recently become clear that there is considerable latitude in the physical condition of gas surrounding the nucleus.For theories of AGN to be presented with a real challenge, we need two things. First, a clear qualitative phenomenology, such as the possibility outlined above, must be decided upon. Second, we need to formulate a quantitative phenomenology.

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Two-phase models of quasar emission line regions

Cited by 480 publications

References 0 publications

XMM–Newtonobservations of the Seyfert 1 galaxy ESO 141–G55

XMM–Newtonobservations of the Seyfert 1 galaxy ESO 141–G55

Variable Ultraviolet Absorption in the Seyfert 1 Galaxy NGC 3516: The Case for Associated Ultraviolet and X‐Ray Absorption

Classification of active galaxies and the prospect of a unified phenomenology

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