Lance Miller

Abstract:

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.

Abstract:

We consider new Suzaku data for NGC3516 taken during 2009 along with other recent X-ray observations of the source. The cumulative characteristics of NGC3516 cannot be explained without invoking changes in the line-of-sight absorption. Contrary to many other well-studied Seyfert galaxies, NGC3516 does not show a positive lag of hard X-ray photons relative to soft photons over the timescales sampled. In the context of reverberation models for the X-ray lags, the lack of such a signal in NGC3516 is consistent with flux variations being dominated by absorption changes. The lack of any reverberation signal in such a highly variable source disfavors intrinsic continuum variability in this case. Instead, the colorless flux variations observed at high flux states for NGC3516 are suggested to be a consequence of Compton-thick clumps of gas crossing the line of sight. © 2011. The American Astronomical Society. All rights reserved..

Abstract:

We present the results of a deep 300ks Chandra High Energy Transmission Grating (HETG) observation of the highly variable narrow-line Seyfert Type 1 galaxy NGC 4051. The HETG spectrum reveals 28 significant soft X-ray ionized lines in either emission or absorption; primarily originating from H-like and He-like K-shell transitions of O, Ne, Mg and Si (including higher order lines and strong forbidden emission lines from Ovii and Neix) plus high-ionization L-shell transitions from Fexvii to Fexxii and lower ionization inner-shell lines (e.g. Ovi). Modelling the data with xstar requires four distinct ionization zones for the gas, all outflowing with velocities < 1000kms -1 . A selection of the strongest emission/absorption lines appear to be resolved with full width at half-maximum (FWHM) of ∼600kms -1 . We also present the results from a quasi-simultaneous 350ks Suzaku observation of NGC 4051 where the X-ray Imaging Spectrometer (XIS) spectrum reveals strong evidence for blueshifted absorption lines at ∼6.8 and ∼7.1keV, consistent with previous findings. Modelling with xstar suggests that this is the signature of a highly ionized, high-velocity outflow (logξ= 4.1 +0.2 -0.1 ; v out ∼-0.02c) which potentially may have a significant effect on the host galaxy environment via feedback. Finally, we also simultaneously model the broad-band 2008 XIS+HXD (Hard X-ray Detector) Suzaku data with archival Suzaku data from 2005 when the source was observed to have entered an extended period of low flux in an attempt to analyse the cause of the long-term spectral variability. We find that we can account for this by allowing for large variations in the normalization of the intrinsic power-law component which may be interpreted as being due to significant changes in the covering fraction of a Compton-thick partial-coverer obscuring the central continuum emission. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

Here we present a number of improvements to weak lensing 3D power spectrum analysis, 3D cosmic shear, that uses the shape and redshift information of every galaxy to constrain cosmological parameters. We show how photometric redshift probability distributions for individual galaxies can be directly included in this statistic with no averaging. We also include the Limber approximation, considerably simplifying full 3D cosmic shear analysis, and we investigate its range of applicability. Finally we show the relationship between weak lensing tomography and the 3D cosmic shear field itself; the steps connecting them being the Limber approximation, a harmonic-space transform and a discretization in wavenumber. Each method has its advantages; 3D cosmic shear analysis allows straightforward inclusion of all relevant modes, thus ensuring minimum error bars, and direct control of the range of physical wavenumbers probed, to avoid the uncertain highly non-linear regime. On the other hand, tomography is more convenient for checking systematics through direct investigation of the redshift dependence of the signal. Finally, for tomography, we suggest that the angular modes probed should be redshift dependent, to recover some of the 3D advantages. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.