Electron-ion coupling in rapidly varying sources

Guilbert, P. W.; Fabian, A. C.; Stepney, Susan

doi:10.1093/mnras/199.1.19p

Cited by 11 publications

(5 citation statements)

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“…This emphasizes the long standing problems of the heating and thermalization process (Guilbert, Fabian & Stepney 1982;Ghisellini, Haardt & Fabian 1993;Svensson 1999;Merloni & Fabian 2001). All sources have a cooling time less than the light crossing time so the energy must be present there in some other form.…”

Section: Discussionmentioning

confidence: 97%

Properties of AGN coronae in theNuSTARera

Fabian

Lohfink

Kara

et al. 2015

Mon. Not. R. Astron. Soc.

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370

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The focussing optics of NuSTAR have enabled high signal-to-noise spectra to be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic Black Hole Binaries (BHB). Spectral modelling then allows robust characterization of the spectral index and upper energy cutoff of the coronal power-law continuum, after accounting for reflection and absorption effects. Spectral-timing studies, such as reverberation and broad iron line fitting, of these sources yield coronal sizes, often showing them to be small and in the range of 3 to 10 gravitational radii in size. Our results indicate that coronae are hot and radiatively compact, lying close to the boundary of the region in the compactness -temperature (Θ − ℓ) diagram which is forbidden due to runaway pair production. The coincidence suggests that pair production and annihilation are essential ingredients in the coronae of AGN and BHB and that they control the shape of the observed spectra.

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Section: Discussionmentioning

confidence: 97%

Properties of AGN coronae in theNuSTARera

Fabian

Lohfink

Kara

et al. 2015

Mon. Not. R. Astron. Soc.

Self Cite

370

433

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“…Many sources are (marginally) above the electron-electron coupling line and all are above the electron-proton line. This emphasizes the long standing problems of the heating and thermalization process (Guilbert, Fabian & Stepney 1982;Ghisellini, Haardt & Fabian 1993;Svensson 1999;Merloni & Fabian 2001). All sources have a cooling time less than the light crossing time so the energy must be present there in some other form.…”

Section: Discussionmentioning

confidence: 97%

Properties of AGN coronae in the NuSTAR era – II. Hybrid plasma

Fabian

Lohfink

Belmont

et al. 2017

Monthly Notices of the Royal Astronomical Society

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130

140

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The corona, a hot cloud of electrons close to the centre of the accretion disc, produces the hard X-ray power-law continuum commonly seen in luminous Active Galactic Nuclei (AGN). The continuum has a high-energy turnover, typically in the range of one to several 100 keV and is suggestive of Comptonization by thermal electrons. We are studying hard X-ray spectra of AGN obtained with NuSTAR after correction for X-ray reflection and under the assumption that coronae are compact, being only a few gravitational radii in size as indicated by reflection and reverberation modelling. Compact coronae raise the possibility that the temperature is limited and indeed controlled by electron-positron pair production, as explored earlier (Paper I). Here we examine hybrid plasmas in which a mixture of thermal and nonthermal particles is present. Pair production from the nonthermal component reduces the temperature leading to a wider temperature range more consistent with observations.

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“…One is because, compared to the corona inside R in , that in the overlapping region must be more strongly cooled by the disk photons, and less efficiently heated by protons due to lower densities. The other is because, at about R cc , the disk surface layer must evaporate into the corona, so it will take a fraction of a second (calculated at R cc ; Guilbert et al 1982) for the evaporated electrons to be heated by protons via Coulomb interaction. Then, the observed T e ∼ 100 keV should be considered as a radial average over the corona.…”

Section: A Possible Interpretation Of the Fast X-ray Variationmentioning

confidence: 99%

Suzaku Results on Cygnus X-1 in the Low/Hard State

Makishima,

Takahashi,

Yamada

et al. 2008

Preprint

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The black-hole binary Cygnus X-1 was observed for 17 ks with the Suzaku X-ray observatory in 2005 October, while it was in a low/hard state with a 0.7-300 keV luminosity of 4.6 × 10 37 erg s −1 . The XIS and HXD spectra, spanning 0.7-400 keV, were reproduced successfully incorporating a cool accretion disk and a hot Comptonizing corona. The corona is characterized by an electron temperature of ∼ 100 keV, and two optical depths of ∼ 0.4 and ∼ 1.5 which account for the harder and softer continua, respectively. The disk has the innermost temperature of ∼ 0.2 keV, and is though to protrude half way into the corona. The disk not only provides seed photons to the Compton cloud, but also produces a soft spectral excess, a mild reflection hump, and a weakly broadened iron line. A comparison with the Suzaku data on GRO J1655−40 reveals several interesting spectral differences, which can mostly be attributed to inclination effects assuming that the disk has a flat geometry while the corona is grossly spherical. An intensity-sorted spectroscopy indicates that the continuum becomes less Comptonized when the source flares up on times scales of 1-200 s, while the underlying disk remains unchanged.Key words: accretion disks -black hole physics -stars: individual (Cygnus X-1)-X-ray: binaries * The HP and LP spectra were fitted simultaneously with the cutoffpl+pexrav model. The reflection strength was fixed at Ω/2π = 0.16 † Constrained to be the same between the HP and LP spectra. ‡ The ratio of cutoffpl normalization (at 1 keV) between HP and LP.

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Electron-ion coupling in rapidly varying sources

Cited by 11 publications

References 0 publications

Properties of AGN coronae in theNuSTARera

Properties of AGN coronae in theNuSTARera

Properties of AGN coronae in the NuSTAR era – II. Hybrid plasma

Suzaku Results on Cygnus X-1 in the Low/Hard State

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