The role of advection in the accreting corona model for active galactic nuclei and Galactic black holes

We consider the role of advection in the two-temperature accreting corona with an underlying optically thick disc. The properties of coronal solutions depend significantly on the description of advection. Local parameterization of advection by a constant coeficient $\delta$ replacing the radial derivatives lead to complex topology of solutions, similar to some extent to other advection-dominated accretion flow solutions. One, radiatively cooled branch exists for low accertion rates. For higher accretion rates two solutions exist in a broad range of radii: one is radiatively cooled and the other one is advection-dominated. With further increase of accretion rate the radial extensions of the two solutions shrink and no solutions are found above certain critical value. However, these trends change if the local parameterization of advection is replaced by proper radial derivatives computed iteratively from the model. Only one, radiatively cooled solution remains, and it exists even for high accretion rates. The advection-dominated branch disappears during the iteration process which means that a self-consistently described advection-dominated flow cannot exist in the presence of an underlying cold disc.Comment: 12 pages, 8 figures, accepted to MNRA

Can the cosmic x ray and gamma ray background be due to reflection of a steep power law spectrum and Compton scattering by relativistic electrons?

We reconsider the recent model for the origin in the cosmic X-ray and gamma-ray background by Rogers and Field. The background in the model is due to an unresolved population of AGNs. An individual AGN spectrum contains three components: a power law with the energy index of alpha = 1.1, an enhanced reflection component, and a component from Compton scattering by relativistic electrons with a low energy cutoff at some minimum Lorentz factor, gamma(sub min) much greater than 1. The MeV bump seen in the gamma-ray background is then explained by inverse Compton emission by the electrons. We show that the model does not reproduce the shape of the observed X-ray and gamma-ray background below 10 MeV and that it overproduces the background at larger energies. Furthermore, we find the assumptions made for the Compton component to be physically inconsistent. Relaxing the inconsistent assumptions leads to model spectra even more different from that of the observed cosmic background. Thus, we can reject the hypothesis that the high-energy cosmic background is due to the described model

On the effect of coronal outflow on spectra formation in galactic black hole systems

We present the results of both analytical and numerical calculations of the amplitude of the reflection component in X-ray spectra of galactic black hole systems. We take into account the anisotropy of Compton scattering and the systematic relativistic bulk motion of the hot plasma. In the case of single scattering approximation the reflection from the disc surface is significantly enhanced due to the anisotropy of Compton scattering. On the other hand the calculations of multiple scattering obtained using the Monte Carlo method show that the anisotropy effect is much weaker in that case. Therefore, the enhanced backscattered flux may affect the observed spectra only if the disc surface is highly ionized, which reduces the absorption in the energy band corresponding to the first Compton scattering.Comment: 8 pages, 8 figures; accepted for publication in MNRA

The dust origin of the Broad Line Region and the model consequences for AGN unification scheme

We propose a very simple physical mechanism responsible for the formation of the Low Ionization Line part of the Broad Line Region in Active Galactic Nuclei. It explains the scaling of the Broad Line Region size with the monochromatic luminosity, including the exact slope and the proportionality constant, seen in the reverberation studies of nearby sources. The scaling is independent from the mass and accretion rate of an active nucleus. The mechanism predicts the formation of a dust-driven wind in the disk region where the local effective temperature of a non-illuminated accretion disk drops below 1000 K and allows for dust formation. We explore now the predictive power of the model with the aim to differentiate between this model and the previously proposed mechanisms of the formation of the Broad Line Region. We discuss the expected departures from the universal scaling at long wavelength, and the role of the inclination angle of the accretion disk in the source. We compare the expected line profiles with Mg II line profiles in the quasars observed by us with the SALT telescope. We also discuss the tests based on the presence or absence of the broad emission lines in low luminosity active galaxies. Finally, we discuss the future tests of the model to be done with expected ground-based observations and satellite missions.Comment: Based the talk presented during the COSPAR 2014 meeting, Advances in Space Research (in press

On variability and spectral distortion of the fluorescent iron lines from black-hole accretion discs

We investigate properties of iron fluorescent line arising as a result of illumination of a black hole accretion disc by an X-ray source located above the disc surface. We study in details the light-bending model of variability of the line, extending previous work on the subject. We indicate bending of photon trajectories to the equatorial plane, which is a distinct property of the Kerr metric, as the most feasible effect underlying reduced variability of the line observed in several objects. A model involving an X-ray source with a varying radial distance, located within a few central gravitational radii around a rapidly rotating black hole, close to the disc surface, may explain both the elongated red wing of the line profile and the complex variability pattern observed in MCG--6-30-15 by XMM-Newton. We point out also that illumination by radiation which returns to the disc (following the previous reflection) contributes significantly to formation of the line profile in some cases. As a result of this effect, the line profile always has a pronounced blue peak (which is not observed in the deep minimum state in MCG--6-30-15), unless the reflecting material is absent within the innermost 2--3 gravitational radii.Comment: 24 pages, 22 figures. Accepted for publication in MNRA