The Structure and Spectral Features of a Thin Disk and Evaporation-Fed Corona in High-Luminosity AGNs

Abstract

We investigate the accretion process in high-luminosity AGNs (HLAGNs) in the scenario of the disk evaporation model. Based on this model, the thin disk can extend down to the innermost stable circular orbit (ISCO) at accretion rates higher than $0.02{\dot{M}}_{\mathrm{Edd}}$; while the corona is weak since part of the coronal gas is cooled by strong inverse Compton scattering of the disk photons. This implies that the corona cannot produce as strong X-ray radiation as observed in HLAGNs with large Eddington ratio. In addition to the viscous heating, other heating to the corona is necessary to interpret HLAGN. In this paper, we assume that a part of accretion energy released in the disk is transported into the corona, heating up the electrons and thereby radiated away. We for the first time, compute the corona structure with additional heating, taking fully into account the mass supply to the corona and find that the corona could indeed survive at higher accretion rates and its radiation power increases. The spectra composed of bremsstrahlung and Compton radiation are also calculated. Our calculations show that the Compton dominated spectrum becomes harder with the increase of energy fraction ($f$) liberating in the corona, and the photon index for hard X-ray($2-10\mathrm{keV}$) is $2.2<\Gamma <2.7$. We discuss possible heating mechanisms for the corona. Combining the energy fraction transported to the corona with the accretion rate by magnetic heating, we find that the hard X-ray spectrum becomes steeper at larger accretion rate and the bolometric correction factor ($L_{\mathrm{bol}}/L_{2-10keV}$) increases with increasing accretion rate for $f<8/35$, which is roughly consistent with the observational results.

39 pages, 10 figures, 1 table, accepted for publication by ApJ

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Cited by in corpus (10)

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• Testing the disk-corona interplay in radiatively-efficient broad-line AGN
• The condensation of the corona for the correlation between the hard X-ray photon index $\Gamma$ and the reflection scaling factor $\Re$ in active galactic nuclei
• The disk evaporation model for the spectral features of low-luminosity active galactic nuclei
• Revisiting the structure and spectrum of the magnetic-reconnection-heated corona in luminous AGNs
• Relationship between X-ray spectral index and X-ray Eddington ratio for Mrk 335 and Ark 564
• Modelling the `outliers' track of the radio--X-ray correlation in X-ray binaries based on disc-corona model
• Microlensing Evidence for Super-Eddington Disc Accretion in Quasars
• Global Transonic Solution of Hot Accretion Flow with Thermal Conduction