Christine Done

Kinematics of the Broad Emission Line Region in NGC 5548

We derive both total flux and velocity-resolved response functions for the CIV 1549 emission line from the data obtained in the 1993 NGC 5548 monitoring campaign. These response functions imply: 1.) the emission region stretches from inside 1 lt-d to outside 10 lt-d, and is probably better described as round than flat; 2.) the velocity field is dominated by a red/blue symmetric component (e.g. 2--d or 3--d random motions, or rotation in a disk) but there is also {\it significant} radial infall. Quantitative modelling indicates that the random speeds are typically a few times as large as the radial speed. However, no simple model gives a completely acceptable fit to the data. These inferences rule out numerous simple and otherwise plausible models for broad line region dynamics, including outflowing winds, radial free-fall, rotation in a disk, or collisionless orbital motion.

Reverberation mapping by regularized linear inversion

Reverberation mapping of active galactic nucleus (AGN) emission-line regions requires the numerical deconvolution of two time series. We suggest the application of a new method, regularized linear inversion, to the solution of this problem. This method possesses many good features; it imposes no restrictions on the sign of the response function; it can provide clearly defined uncertainty estimates; it involves no guesswork about unmeasured data; it can give a clear indication of when the underlying convolution model is inadequate; and it is computationally very efficient. Using simulated data, we find the minimum S/N and length of the time series in order for this method to work satisfactorily. We also define guidelines for choosing the principal tunable parameter of the method and for interpreting the results. Finally, we reanalyze published data from the 1989 NGC 5548 campaign using this new method and compare the results to those previously obtained by maximum entropy analysis. For some lines we find good agreement, but for others, especially C III lambda(1909) and Si IV lambda(1400), we find significant differences. These can be attributed to the inability of the maximum entropy method to find negative values of the response function, but also illustrate the nonuniqueness of any deconvolution technique. We also find evidence that certain line light curves (e.g., C IV lambda(1549)) cannot be fully described by the simple linear convolution model.

Evidence for an ionized reprocessor in NGC 6814

A detailed spectroscopic analysis of a Ginga observation of the Seyfert galaxy NGC 6814 is reported. It is shown that the X-ray data are consistent with a scenario in which the continuum radiation is reprocessed in a highly ionized medium, which can either be an accretion disk or a shell of absorbing material. Both of these can produce the strong observed iron K-alpha line, which must originate within 200 lt-sec of the continuum source. Significant iron K-beta and nickel K-alpha are predicted, based on the iron K-alpha line strength, and these lines partially conceal the iron edge in this source. The spectral variability below about 4 keV, where the apparent absorption increases as the continuum flux decreases, is probably caused by a warm absorber covering the reprocessing system.

The origin of [Fe ii] emission in NGC 4151

The centre of NGC 4151 has been observed in the J band with the SMIRFS integral field unit (IFU) on the UK Infrared Telescope. A map of [Fe ii] emission is derived, and compared with the distributions of the optical narrow-line region and radio jet. We conclude that, because the [Fe ii] emission is associated more closely with the visible narrow-line region than with the radio jet, it arises mainly through photoionization of gas by collimated X-rays from the Seyfert nucleus. The velocity field and strength with respect to Paβ are found to be consistent with this argument. The performance of the IFU is considered briefly, and techniques for observation and data analysis are discussed.

The X‐ray Variability of NGC 4945: Characterizing the Power Spectrum through Light Curve Simulations

For light curves sampled on an uneven grid of observation times, the shape of the power density spectrum (PDS) includes severe distortion effects due to the window function, and simulations of light curves are indispensable to recover the true PDS. We present an improved method for comparing light curves generated from a PDS model to the measured data and apply it to a 50‐day long RXTE observations of NGC 4945, a Seyfert 2 galaxy with well‐determined mass from megamaser observations. The improvements over previously reported investigations include the adjustment of the PDS model normalization for each simulated light curve in order to directly investigate how well the chosen PDS shape describes the source data. We furthermore implement a robust goodness‐of‐fit measure that does not depend on the form of the variable used to describe the power in the periodogram. We conclude that a knee‐type function (smoothly broken power law) describes the data better than a simple power law; the best‐fit break frequency...

RECENT RESULTS FOR AGN OBSERVED BY THE ROSSI X-RAY TIMING EXPLORER

Abstract The Rossi X-ray Timing Explorer (RXTE) has produced many excellent observations of active galaxies, providing so far the best sensitivity over the bandpass of 10 – 20 keV. This paper reports selected RTXE data for X-ray bright Seyfert galaxies in the context of the currently popular models. One is the recent result for two Seyfert 1 galaxies, NGC 5548 and IC 4329a: both show the “canonical” Seyfert 1 X-ray spectra, with an underlying power law, plus iron Kα fluorescence line and Compton reflection. Interestingly, in both cases, the profile of the Fe K line does not extend as far to the red as seen in the famous MCG-6-30-15, and this indicates that the regions where the Fe K lines originate in AGN are diverse. Independently, in both objects we see a strong spectral variability of the primary continua, which soften as the sources brighten. The second result is for the heavily absorbed Seyfert 2 NGC 4945. The RXTE data confirm the strong absorption corresponding to the optical depth to electron scattering of about 2, but also reveal rapid variability of the hard (8 – 30 keV) X-ray emission on a time scale of a day or less. This suggests that for NGC 4945, the putative parsec-size molecular torus cannot be both geometrically and optically thick. It also implies that if the Cosmic X-ray Background is made up of heavily absorbed sources, they are unlikely to have the absorber confined to a geometrically thin disk as inferred for NGC 4945.