X-ray reverberation in NLS1

Reverberation from scattering material around the black hole in active galactic nuclei is expected to produce a characteristic signature in a Fourier analysis of the time delays between directly-viewed continuum emission and the scattered light. Narrow-line Seyfert 1 galaxies (NLS1) are highly variable at X-ray energies, and are ideal candidates for the detection of X-ray reverberation. We show new analysis of a small sample of NLS1 that clearly shows the expected time-delay signature, providing strong evidence for the existence of a high covering fraction of scattering and absorbing material a few tens to hundreds of gravitational radii from the black hole. We also show that an alternative interpretation of time delays in the NLS1 1H0707-495, as arising about one gravitational radius from the black hole, is strongly disfavoured in an analysis of the energy-dependence of the time delays.Comment: Published online in Proceedings of Science, "Narrow-line Seyfert 1 Galaxies and their place in the Universe", held in Milan, Italy April 4-6, 201

The hard X-ray spectrum of NGC 1365: scattered light, not black hole spin

Active Galactic Nuclei (AGN) show excess X-ray emission above 10 keV compared with extrapolation of spectra from lower energies. Risaliti et al. have recently attempted to model the hard X-ray excess in the type 1.8 AGN NGC 1365, concluding that the hard excess most likely arises from Compton-scattered reflection of X-rays from an inner accretion disk close to the black hole. Their analysis disfavored a model in which the hard excess arises from a high column density of circumnuclear gas partially covering a primary X-ray source, despite such components being required in the NGC 1365 data below 10 keV. Using a Monte Carlo radiative transfer approach, we demonstrate that this conclusion is invalidated by (i) use of slab absorption models, which have unrealistic transmission spectra for partial covering gas, (ii) neglect of the effect of Compton scattering on transmitted spectra and (iii) inadequate modeling of the spectrum of scattered X-rays. The scattered spectrum is geometry dependent and, for high global covering factors, may dominate above 10 keV. We further show that, in models of circumnuclear gas, the suppression of the observed hard X-ray flux by reprocessing may be no larger than required by the `light bending' model invoked for inner disk reflection, and the expected emission line strengths lie within the observed range. We conclude that the time-invariant `red wing' in AGN X-ray spectra is probably caused by continuum transmitted through and scattered from circumnuclear gas, not by highly redshifted line emission, and that measurement of black hole spin is not possible.Comment: Revised version, accepted for publication by Ap.J. Letter

X-ray Signatures of Circumnuclear Gas in AGN

X-ray spectra of AGN are complex. X-ray absorption and emission features trace gas covering a wide range of column densities and ionization states. High resolution spectra show the absorbing gas to be outflowing, perhaps in the form of an accretion disk wind. The absorbing complex shapes the form of the X-ray spectrum while X-ray reverberation and absorption changes explain the spectral and timing behaviour of AGN. We discuss recent progress, highlighting some new results and reviewing the implications that can be drawn from the data.Comment: Proceedings of the conference "Suzaku 2011, Exploring the X-ray Universe: Suzaku and Beyond

Dust Transport in Protostellar Disks Through Turbulence and Settling

We apply ionization balance and MHD calculations to investigate whether magnetic activity moderated by recombination on dust can account for the mass accretion rates and the mid-infrared spectra and variability of protostellar disks. The MHD calculations use the stratified shearing-box approach and include grain settling and the feedback from the changing dust abundance on the resistivity of the gas. The two-decade spread in accretion rates among T Tauri stars is too large to result solely from variety in the grain size and stellar X-ray luminosity, but can be produced by varying these together with the disk magnetic flux. The diversity in the silicate bands can come from the coupling of grain settling to the distribution of the magneto-rotational turbulence, through three effects: (1) Recombination on grains yields a magnetically inactive dead zone extending above two scale heights, while turbulence in the magnetically active disk atmosphere overshoots the dead zone boundary by only about one scale height. (2) Grains deep in the dead zone oscillate vertically in waves driven by the turbulent layer above, but on average settle at the laminar rates, so the interior of the dead zone is a particle sink and the disk atmosphere becomes dust-depleted. (3) With sufficient depletion, the dead zone is thinner and mixing dredges grains off the midplane. The MHD results also show that the magnetic activity intermittently lifts clouds of dust into the atmosphere. The photosphere height changes by up to one-third over a few orbits, while the extinction along lines of sight grazing the disk surface varies by factors of two over times down to 0.1 orbit. We suggest that the changing shadows cast by the dust clouds on the outer disk are a cause of the daily to monthly mid-infrared variability in some young stars. (Abridged.)Comment: ApJ in pres

Transient Relativistically-Shifted Lines as a Probe of Black Hole Systems

X-ray spectra of Seyfert galaxies have revealed a new type of X-ray spectral feature, one which appears to offer important new insight into the black hole system. XMM/Chandra revealed several narrow emission lines redward of Fe Kalpha in NGC 3516. Since that discovery the phenomenon has been observed in other Seyfert galaxies, e.g. NGC 7314 and ESO 198-G24. We present new evidence for a redshifted Fe line in XMM spectra of Mrk 766. These data reveal the first evidence for a significant shift in the energy of such a line, occurring over a few tens of kiloseconds. This shift may be interpreted as deceleration of an ejected blob of gas traveling close to the escape velocity.Comment: 13 pages, 5 figures (4 color) accepted by Ap

Skylab food system

A review of the Skylab food system requirements, package designs, and launch configurations was presented. In-flight anomalies were discussed, and between-mission changes in design were described. A discussion of support for Skylab 3 and Skylab 4 mission extensions and of new items launched on these missions is included

Akn 564: an unusual component in the X-ray spectra of NLSy1 galaxies

We present an ASCA observation of the NLSy1 Ark 564. The X-ray light curve shows rapid variability, but no evidence for energy-dependence to these variations, within the 0.6 -- 10 keV bandpass. A strong (EW ~ 70 eV) spectral feature is observed close to 1 keV. A similar feature has been observed in TON S180 (another NLSy1) but has not been observed in broad-line Seyfert galaxies. The feature energy suggests a large contribution from Fe L-shell lines but its intensity is difficult to explain in terms of emission and/or absorption from photoionized gas. Models based on gas in thermal equilibrium with kT ~1 keV provide an alternative parameterization of the soft spectrum. The latter may be interpreted as the hot intercloud medium, undergoing rapid cooling and producing strong Fe L-shell recombination lines. In all cases the physical conditions are rather different from those observed in broad-line Seyferts. The hard X-ray spectrum shows a broad and asymmetric Fe Kalpha line of large equivalent width (~550 eV) which can be explained by a neutral disk viewed at ~ 60 degrees to the line-of-sight, contrary to the hypothesis that NLSy1s are viewed pole-on. The large EW of this line, the strong 1 keV emission and the strong optical Fe emission lines all suggest an extreme Fe abundance in this and perhaps other NLSy1s.Comment: 15 pages, 5 figures. LaTeX with encapsulated postscript. Accepted for publication in the Astrophysical Journa