An Introduction to Active Galactic Nuclei

Peterson, Bradley M.

doi:10.1017/cbo9781139170901

Cited by 703 publications

(462 citation statements)

References 21 publications

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“…The fundamental issue is the solid angle subtended by the stream relative to the black hole, where the typical estimate for a normal quasar is that the broad line clouds have a covering fraction of order f ≃ 10% (e.g. Peterson 1997). The structure of the debris orbits leads to a roughly constant angular width in the orbital plane as seen from the black hole (see, e.g., Kochanek 1994).…”

Section: Abundance Anomalies In Tdesmentioning

confidence: 99%

“…From §2, it is clear that TDEs provide a natural source of nitrogen-rich, carbon-poor material -the disruption of a single star easily provides sufficient mass to pollute the broad line region (BLR) of a quasar, since the mass in the BLR is only ∼ 10 −3 M⊙ (e.g. Peterson 1997). The challenge is that, at least for Q0353−383, the anomalous spectra can persist for decades (Osmer 1980, Baldwin et al 2003.…”

Section: Nitrogen Rich Quasars and Tdesmentioning

confidence: 99%

“…The one interesting loophole is the observation by Arcavi et al (2014) that a large fraction (∼ 90%) of TDEs seem to be in post starburst galaxies, which otherwise represent only ∼ 1% of galaxies (e.g., Quintero et al 2004). Assuming post starburst galaxies represent recent mergers, and that mergers also are an important trigger of quasar activity (e.g.…”

Section: Nitrogen Rich Quasars and Tdesmentioning

confidence: 99%

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Abundance anomalies in tidal disruption events

Kochanek

2016

Mon. Not. R. Astron. Soc.

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The ∼ 10% of tidal disruption events (TDEs) due to stars more massive than M * > ∼ M ⊙ should show abundance anomalies due to stellar evolution in helium, carbon and nitrogen, but not oxygen. Helium is always enhanced, but only by up to ∼ 25% on average because it becomes inaccessible once it is sequestered in the high density core as the star leaves the main sequence. However, portions of the debris associated with the disrupted core of a main sequence star can be enhanced in helium by factors of 2-3 for debris at a common orbital period. These helium abundance variations may be a contributor to the observed diversity of hydrogen and helium line strengths in TDEs. A still more striking anomaly is the rapid enhancement of nitrogen and the depletion of carbon due to the CNO cycle -stars with M * > ∼ M ⊙ quickly show an increase in their average N/C ratio by factors of 3-10. Because low mass stars evolve slowly and high mass stars are rare, TDEs showing high N/C will almost all be due to 1-2M ⊙ stars disrupted on the main sequence. Like helium, portions of the debris will show still larger changes in C and N, and the anomalies decline as the star leaves the main sequence. The enhanced [N/C] abundance ratio of these TDEs provides the first natural explanation for the rare, nitrogen rich quasars and also explains the strong nitrogen emission seen in ultraviolet spectra of ASASSN-14li.

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Section: Abundance Anomalies In Tdesmentioning

confidence: 99%

Section: Nitrogen Rich Quasars and Tdesmentioning

confidence: 99%

Section: Nitrogen Rich Quasars and Tdesmentioning

confidence: 99%

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Abundance anomalies in tidal disruption events

Kochanek

2016

Mon. Not. R. Astron. Soc.

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“…A typical local Active Galactic Nucleus (AGN) consumes about 0.01 M ⊙ of fuel per year (e.g. [12]), most likely coming from gas inflow. This corresponds to about 10 6 M ⊙ during its 10 8 -yr long activity.…”

Section: Nuclear Spiral As a Feeding Mechanism Of The Mbhmentioning

confidence: 99%

Nuclear Spirals in Galaxies

Maciejewski¹

2008

Mapping the Galaxy and Nearby Galaxies

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Summary. Recent high-resolution observations indicate that nuclear spirals are often present in the innermost few hundred parsecs of disc galaxies. My models show that nuclear spirals form naturally as a gas response to non-axisymmetry in the gravitational potential. Some nuclear spirals take the form of spiral shocks, resulting in streaming motions in the gas, and in inflow comparable to the accretion rates needed to power local Active Galactic Nuclei. Recently streaming motions of amplitude expected from the models have been observed in nuclear spirals, confirming the role of nuclear spirals in feeding of the central massive black holes.

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“…According to this scheme, intense X-rays originate just a few gravitational radii from the black hole horizon. Manifestation of strong gravity has been searched in X-ray spectra of AGN with the main aim of finding the firm evidence for the central black hole (BH) and determining its parameters, namely, mass and angular momentum (for a detailed exposition of the subject, see Peterson 1997;Krolik 1999).…”

Section: Introductionmentioning

confidence: 99%

Theoretical aspects of relativistic spectral features

Karas

2006

Astron Nachr

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The inner parts of black-hole accretion discs shine in X-rays which can be monitored and the observed spectra can be used to trace strong gravitational fields in the place of emission and along paths of light rays. This paper summarizes several aspects of how the spectral features are influenced by relativistic effects. We focus our attention onto variable and broad emission lines, origin of which can be attributed to the presence of orbiting patterns -spots and spiral waves in the disc. We point out that the observed spectrum can determine parameters of the central black hole provided the intrinsic local emissivity is constrained by theoretical models.

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An Introduction to Active Galactic Nuclei

Cited by 703 publications

References 21 publications

Abundance anomalies in tidal disruption events

Abundance anomalies in tidal disruption events

Nuclear Spirals in Galaxies

Theoretical aspects of relativistic spectral features

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