X-ray Reflection from Inhomogeneous Accretion Disks: II. Emission Line Variability and Implications for Reverberation Mapping

One of the principal scientific objectives of the upcoming Constellation-X mission is to attempt to map the inner regions of accretion disks around black holes in Seyfert galaxies by reverberation mapping of the Fe K fluorescence line. This area of the disk is likely radiation pressure dominated and subject to various dynamical instabilities. Here, we show that density inhomogeneities in the disk atmosphere resulting from the photon bubble instability (PBI) can cause rapid changes in the X-ray reflection features, even when the illuminating flux is constant. Using a simulation of the development of the PBI, we find that, for the disk parameters chosen, the Fe K and O VIII Ly\alpha lines vary on timescales as short as a few hundredths of an orbital time. In response to the changes in accretion disk structure, the Fe K equivalent width (EW) shows variations as large as ~100 eV. The magnitude and direction (positive or negative) of the changes depends on the ionization state of the atmosphere. The largest changes are found when the disk is moderately ionized. The O VIII EW varies by tens of eV, as well as exhibiting plenty of rapid, low-amplitude changes. This effect provides a natural explanation for some observed instances of short timescale Fe K variability which was uncorrelated with the continuum (e.g., Mrk 841). New predictions for Fe K reverberation mapping should be made which include the effects of this accretion disk driven line variability and a variable ionization state. Reflection spectra averaged over the evolution of the instability are well fit by constant density models in the 2-10 keV region.Comment: 20 pages, 3 figures. Accepted by Ap

The absorption-dominated model for the X-ray spectra of type I active galaxies: MCG-6-30-15

MCG-6-30-15 is the archetypal example of a type I active galaxy showing broad "red-wing" emission in its X-ray spectrum at energies below the 6.4 keV Fe K-alpha emission line and a continuum excess above 20 keV. Miller et al. (2008) showed that these spectral features could be caused by clumpy absorbing material, but Reynolds et al. (2009) have argued that the observed Fe K-alpha line luminosity is inconsistent with this explanation unless the global covering factor of the absorber(s) is very low. However, the Reynolds et al. calculation effectively considers the only source of opacity to be the Fe K bound-free transition and neglects the opacity at the line energy: correction to realistic opacity decreases the predicted line flux by a large factor. We also discuss the interpretation of the covering factor and the possible effect of occultation by the accretion disk. Finally, we consider a model for MCG-6-30-15 dominated by clumpy absorption, which is consistent with global covering factor 0.45, although models that include the effects of Compton scattering are required to reach a full understanding. Variations in covering fraction may dominate the observed X-ray spectral variability.Comment: Accepted for publication in MNRAS letter

RAiSE III : 3C radio AGN energetics and composition

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Kinetic jet power estimates based exclusively on observed monochromatic radio luminosities are highly uncertain due to confounding variables and a lack of knowledge about some aspects of the physics of active galactic nuclei (AGNs). We propose a new methodology to calculate the jet powers of the largest, most powerful radio sources based on combinations of their size, lobe luminosity, and shape of their radio spectrum; this approach avoids the uncertainties encountered by previous relationships. The outputs of our model are calibrated using hydrodynamical simulations and tested against independent X-ray inverse-Compton measurements. The jet powers and lobe magnetic field strengths of radio sources are found to be recovered using solely the lobe luminosity and spectral curvature, enabling the intrinsic properties of unresolved high-redshift sources to be inferred. By contrast, the radio source ages cannot be estimated without knowledge of the lobe volumes. The monochromatic lobe luminosity alone is incapable of accurately estimating the jet power or source age without knowledge of the lobe magnetic field strength and size, respectively. We find that, on average, the lobes of the Third Cambridge Catalogue of Radio Sources (3C) have magnetic field strengths approximately a factor three lower than the equipartition value, inconsistent with equal energy in the particles and the fields at the 5σ level. The particle content of 3C radio lobes is discussed in the context of complementary observations; we do not find evidence favouring an energetically dominant proton population.Peer reviewe

The impact of General Dental Council registration and continuing professional development on UK dental care professionals:(1) dental nurses.

Objective To investigate the impact of GDC registration and mandatory CPD on dental nurses’ views, job satisfaction and intention to leave. Design Postal/online survey, conducted in parallel with a survey of dental technicians. Setting UK private and NHS practices, community services, dental hospitals. Subjects and methods Representative sample of General Dental Council registrants. Main outcome measures Job satisfaction; intention to leave profession (dependent variable in regression analysis). Results Eleven were ineligible (left profession, moved abroad); 267 (44% of those eligible) responded, all female. Respondents’ mean age was 38.2 years (sd 10.74). The general principle of registration was endorsed by 67%, and compulsory registration by 51%, but the fee level by only 6%. Most nurses did not feel that registration had affected their view of dental nursing as a career (56%), their role (74%) or status (86%) within the dental team, or that CPD helped them to do their job better (76%). Fiftly-six percent were not satisfied with their job, and 22% intended to leave the profession. Intention to leave was predicted by younger age and greater dissatisfaction with physical working conditions and opportunities to progress. Conclusions Widely held criticisms regarding the costs and relevance of registration and CPD coupled with a potentially high level of attrition from the profession suggest a review of the fee and salary structure and greater financial support for CPD is warranted