A model for the X-ray and ultraviolet emission from Seyfert galaxies and galactic black holes

TLDR

Blob‑powered Comptonization can dominate the intrinsic disk radiation in radio‑quiet AGN and galactic black holes. The authors propose that X‑ray emission arises from Comptonization of disk photons in localized blobs and examine the resulting UV–X‑ray spectra and light‑curve correlations. They estimate blob properties using an αΩ dynamo accretion‑disk model and determine electron temperatures and spectra analogously to the homogeneous Haardt–Maraschi framework. The model predicts that the emitted spectrum is largely independent of the fraction of gravitational power in blobs, that the X‑ray spectrum hardens with blob form factor, and that un‑intercepted UV luminosity can exceed the X‑ray luminosity, with blob estimates matching observations. Published in ApJ Letters (1994), DOI 10.1086/187520, arXiv:astro‑ph/9405059.

Abstract

view Abstract Citations (367) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Model for the X-Ray and Ultraviolet Emission from Seyfert Galaxies and Galactic Black Holes Haardt, Francesco ; Maraschi, Laura ; Ghisellini, Gabriele Abstract We propose that the X-ray emission from radio-quiet active galactic nuclei and galactic black holes is due to Comptonization of soft thermal photons emitted by the underlying accretion disk in localized structures (blobs). The power per unit area produced by the blobs, impinging on the disk, can easily dominate the radiation internally produced by the disk. In this case the electron temperature and the high-energy spectrum can be determined in a similar way to that used in the previously studied homogeneous model (Haardt & Maraschi 1991). However, in the present model, (a) the emitted spectrum is largely independent of the fraction of gravitational power dissipated in the blobs; (b) the X-ray spectrum can be harder depending on a form factor of the blobs; (c) the UV (or soft X- ray for galactic objects) luminosity that is not intercepted by the blobs can be larger than the X-ray luminosity. In the framework of a simplified accretion disk αOMEGA dynamo model, we make order-of-magnitude estimates of the number of active blobs, their size, their luminosity, and hence their compactness, finding values in agreement with what is observed. The expected UV to X-ray spectra and correlations of X-ray and UV light curves are discussed. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/187520 arXiv: arXiv:astro-ph/9405059 Bibcode: 1994ApJ...432L..95H Keywords: Accretion Disks; Active Galactic Nuclei; Astronomical Models; Black Holes (Astronomy); Compton Effect; Plasma Clouds; Seyfert Galaxies; Ultraviolet Emission; Ultraviolet Spectra; X Ray Spectra; X Rays; Dynamo Theory; Electron Energy; Gravitational Effects; Light Curve; Luminosity; Size Determination; Astrophysics; ACCRETION; ACCRETION DISKS; PLASMAS; RADIATION MECHANISMS: THERMAL; GALAXIES: SEYFERT; X-RAYS: GENERAL; Astrophysics E-Print: 10 pages. Plain Tex. Accepted in ApJ Letters full text sources arXiv | ADS | data products SIMBAD (2)