Slim-Disk Model for Soft X-Ray Excess and Variability of Narrow-Line Seyfert 1 Galaxies

Abstract

Narrow-line Seyfert 1 galaxies (NLS1s) exhibit extreme soft X-ray excess and large variability. We argue that both features can be basically accounted for by the slim disk model. We assume that a central black-hole mass in NLS1 is relatively small, M ∼ 10 5−7 M ⊙ , and that a disk shines nearly at the Eddington luminosity, L E . Then, the disk becomes a slim disk and exhibits the following distinctive signatures: (1) The disk luminosity (particularly of X-rays) is insensitive to mass-flow rates,Ṁ , since the generated energy is partly carried away to the black hole by trapped photons in accretion flow. (2) The spectra are multi-color blackbody. The maximum blackbody temperature is T bb ≃ 0.2(M/10 5 M ⊙ ) −1/4 keV, and the size of the blackbody emitting region is small, r bb < ∼ 3r S (with r S being Schwarzschild radius) even for a Schwarzschild black hole. (3) All the ASCA observation data of NLS1s fall onto the region ofṀ /(L E /c 2 ) > 10 (with L E being the Eddington luminosity) on the (r bb , T bb ) plane, supporting our view that a slim disk emits soft X-rays at ∼ L E in NLS1s. (4) Magnetic energy can be amplified, at most, up to the equipartition value with the trapped radiation energy which greatly exceeds radiation energy emitted from the disk. Hence, energy release by consecutive magnetic reconnection will give rise to substantial variability in soft X-ray emission.

Simulating the growth of intermediate-mass black holes

“…In these radiatively inefficient models the radiation is trapped (see also the diffusion condition in Appendix) into the high-density gas and is advected inward by the accretion flow: this happens when the photon diffusion time exceeds the time scale for accretion. This would allow a very mild dependence of the emitted luminosity L on the normalized accretion rate f Edd , which is usually described as a logarithmic relation (Mineshige et al 2000;Wang & Netzer 2003):…”

“…An early phase of stable super-critical quasi-spherical accretion in the BHs was also proposed in Volonteri & Rees (2005). Such large accretion rates may be sustainable in the so-called "slim disk" solution (Begelman & Meier 1982;Paczynski & Abramowicz 1982;Mineshige et al 2000;Sadowski 2009Sadowski , 2011, an energy-advecting, optically thick accretion flow that generalize the standard thin disk model (Shakura & Sunyaev 1976). In these radiatively inefficient models the radiation is trapped into the high-density gas and is advected inward by the accretion flow: as a consequence, the luminosity is only mildly dependent on the accretion rate and very large flows are sustainable.…”

The X-ray luminous galaxies optically classified as star forming are mostly narrow line Seyfert 1 s

“…Such high temperatures could be explained by the presence of a slim accretion disc in which the temperature is raised by photon trapping (Abramowicz et al 1988;Mineshige et al 2000). For another third of the missing-AGN subsample (second part of the Table 4), the best-fit models were achieved by the addition of a PCF component.…”

Hubble Space TelescopeSTIS Ultraviolet Spectral Evidence of Outflow in Extreme Narrow‐Line Seyfert 1 Galaxies. I. Data and Analysis

“…This pervasiveness leads us to believe that we are observing the manifestation of a primary physical parameter. A favored explanation is that it is the accretion rate relative to the black hole mass onto the active nucleus (e.g., Boller et al 1996;Pounds et al 1995Pounds et al , 2001Comastri et al 1998;Leighly 1999aLeighly , 1999bMathur 2000;Mineshige et al 2000;Kuraszkiewicz et al 2000;Puchnarewicz et al 2001;Ballantyne et al 2001;Boroson 2002;Crenshaw et al 2003).…”