Is the Accretion Flow in NGC 4258 Advection Dominated?

Lasota, Jean–Pierre; Abramowicz, Marek A.; Chen, X.; Krolik, Julian H.; Narayan, Ramesh; Yi, Insu

doi:10.1086/177137

Cited by 233 publications

(270 citation statements)

References 27 publications

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“…These should be particularly relevant to transient binaries. In quiescence, their inner disk regions are described well by optically thin advection-dominated accretion flows (ADAFs; see e.g., Lasota et al 1996;Dubus et al 2001). However, a few black hole systems (e.g., GRS 1915+105 and LMC X-3) have been observed in thermal states corresponding to disk luminosities higher than 0.3L Edd (McClintock & Remillard 2003;Steiner et al 2010), and modeling these require optically thick models going beyond the standard thin disks.…”

Section: Discussionmentioning

confidence: 99%

Relativistic slim disks with vertical structure

Sądowski

Abramowicz

Bursa

et al. 2011

A&A

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135

147

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We report on a scheme for incorporating vertical radiative energy transport into a fully relativistic, Kerr-metric model of optically thick, advective, transonic alpha disks. Our code couples the radial and vertical equations of the accretion disk. The flux was computed in the diffusion approximation, and convection is included in the mixing-length approximation. We present the detailed structure of this "two-dimensional" slim-disk model for α = 0.01. We then calculated the emergent spectra integrated over the disk surface. The values of surface density, radial velocity, and the photospheric height for these models differ by 20%-30% from those obtained in the polytropic, height-averaged slim disk model considered previously. However, the emission profiles and the resulting spectra are quite similar for both types of models. The effective optical depth of the slim disk becomes lower than unity for high values of the alpha parameter and for high accretion rates.

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Section: Discussionmentioning

confidence: 99%

Relativistic slim disks with vertical structure

Sądowski

Abramowicz

Bursa

et al. 2011

A&A

Self Cite

135

147

View full text Add to dashboard Cite

show abstract

“…Irrespective of the detail, the outer cold disc in this scenario is expected to be truncated (Done et al 2007;Gilfanov 2010;Yuan & Narayan 2014). The truncation is also required in early stages of an outburst, given that the disc in quiescence does not extend down to the ISCO (Lasota, Narayan & Yi 1996). When the accretion rate increases further, the truncation radius decreases, the disc starts to penetrate the inner flow and eventually reaches the ISCO in the high/soft state (Remillard & McClintock 2006;Done et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Spectral analysis of theXMM–Newtondata of GX 339–4 in the low/hard state: disc truncation and reflection

Basak¹,

Zdziarski²

2016

Mon. Not. R. Astron. Soc.

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We analyse all available observations of GX 339-4 by XMM-Newton in the hard spectral state. We jointly fit the spectral data by Comptonization and the currently best reflection code, relxill. We consider in detail a contribution from a standard blackbody accretion disc, testing whether its inner radius can be set equal to that of the reflector. However, this leads to an unphysical behaviour of the disc truncation radius, implying the soft X-ray component is not a standard blackbody disc. This appears to be due to irradiation by the hard X-rays, which strongly dominate the total emission. We consider a large array of models, testing, e.g., the effects of the chosen energy range, of adding unblurred reflection, and assuming a lamppost geometry. We find the effects of relativistic broadening to be relatively weak in all cases. In the coronal models, we find the inner radius to be large. In the lamppost model, the inner radius is unconstrained, but when fixed to the innermost stable orbit, the height of the source is large, which also implies a weak relativistic broadening. In the former models, the inner radius correlates with the X-ray hardness ratio, which is consistent with the presence of a truncated disc turning into a complete disc in the soft state. We also find the degree of the disc ionization to anti-correlate with the hardness, leading to strong spectral broadening due to scattering of reflected photons in the reflector in the softest studied states.

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“…That is, an ADAF with a surrounding optically thick disk is found to be necessary in modeling the broadband spectrum from the radio to X-ray energy regime of LLAGNs (Lasota et al 1996;Quataert et al 1999;Di Matteo et al 2000Yuan et al 2009;Li et al 2009;Nemmen et al 2006Nemmen et al , 2012. The need for this truncation derives from both the continuum and line emission and, at times, from their variability.…”

Section: Introductionmentioning

confidence: 99%

Disk Corona Interaction: Mechanism for the Disk Truncation and Spectrum Change in Low-Luminosity Active Galactic Nuclei

Taam

Liu

Yuan

et al. 2012

ApJ

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The truncation of an optically thick, geometrically thin accretion disk is investigated in the context of low-luminosity AGNs (LLAGNs). We generalize the disk evaporation model used in the interpretative framework of black hole X-ray binaries by including the effect of a magnetic field in accretion disks surrounding supermassive black holes. The critical transition mass accretion rate for which the disk is truncated is found to be insensitive to magnetic effects, but its inclusion leads to a smaller truncation radius in comparison to a model without its consideration. That is, a thin viscous disk is truncated for LLAGNs at an Eddington ratio less than 0.03 for a standard viscosity parameter (α = 0.3). An increase of the viscosity parameter results in a higher critical transition mass accretion rate and a correspondingly smaller truncation distance, the latter accentuated by greater magnetic energy densities in the disk. Based on these results, the truncation radii inferred from spectral fits of LLAGNs published in the literature are consistent with the disk evaporation model. The infrared emission arising from the truncated geometrically thin accretion disks may be responsible for the red bump seen in such LLAGNs.

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Is the Accretion Flow in NGC 4258 Advection Dominated?

Cited by 233 publications

References 27 publications

Relativistic slim disks with vertical structure

Relativistic slim disks with vertical structure

Spectral analysis of theXMM–Newtondata of GX 339–4 in the low/hard state: disc truncation and reflection

Disk Corona Interaction: Mechanism for the Disk Truncation and Spectrum Change in Low-Luminosity Active Galactic Nuclei

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