Related papers: Ubiquitous column density variability in Seyfert 2…
Current X-ray observatories make it possible to follow the evolution of transient and variable X-ray binaries across a broad range in luminosity and source behavior. In such studies, it can be unclear whether evolution in the low energy…
Narrow-line Seyfert\,1 galaxies (NLS1s) with very small broad-line widths (say, FWHM(\hb) $\la $ 1200\,\kms) represent the extreme type of Seyfert\,1 galaxies that have small black hole masses (\mbh) and/or high Eddington ratios (\redd).…
We present multiple Chandra and XMM-Newton observations of the type 1.8 Seyfert Galaxy NGC 1365, which shows the most dramatic X-ray spectral changes observed so far in an AGN: the source switched from reflection dominated to transmission…
Strongly magnetized, accreting neutron stars show periodic and aperiodic variability over a wide range of time scales. By obtaining spectral and timing information on these different time scales, we can have a closer look into the physics…
We present a detailed re-analysis of the two {\it ASCA} Performance Verification observations of the nearby Seyfert 1 galaxy MCG-6-30-15. Confirming the results of Fabian et al. (1994), we find definite evidence for the {\sc O\,vii} and…
Warm absorbers are an important new tool for investigating the conditions within the central regions of active galaxies. They have been observed in ~50% of the well-studied Seyfert galaxies and have also been detected in quite a number of…
We present echelle observations of the intrinsic UV absorption lines in the Seyfert galaxy NGC 4151, which were obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope on 1999 July 19. The UV continuum…
There are several Seyfert galaxies for which there is a discrepancy between the small column of neutral hydrogen deduced from X-ray observations and the much greater column derived from the reddening of the optical/UV emission lines and…
This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting the single galaxies in the sample of Heckman et al. (1995) with composite models (shock+ photoionization from the active center), we show that five main…
The morphology of the circumnuclear gas accreting onto supermassive black holes in Seyfert galaxies remains a topic of much debate. As the innermost regions of Active Galactic Nuclei (AGN) are spatially unresolved, X-ray spectroscopy, and…
The $BeppoSAX$ archive is currently the largest reservoir of high sensitivity simultaneous soft and hard-X ray data of Seyfert galaxies. From this database all the Seyfert galaxies (105 objects of which 43 are type I and 62 are type II)…
As a class, LINERs and Low-Luminosity AGN tend to show little or no significant short-term variability (i.e., with time-scales less than a day). This is a marked break for the trend of increased variability in Seyfert 1 galaxies with…
We present the results of our monitoring program to study the long-term variability of the Halpha line in high-mass X-ray binaries. We have carried out the most complete optical spectroscopic study of the global properties of high-mass…
We measured the galactic hydrogen column densities to the neutron-star binaries GX 17+2, 4U 1705-44, and 4U 1728-34 by modeling the Mg and Si absorption edges found in high-resolution X-ray spectra obtained by the Chandra X-ray Observatory.…
We report on the results of a three-year program of coordinated X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray spectra are not detected in the optical,…
We present Suzaku observations of five hard X-ray selected nearby Seyfert 2 galaxies. All the sources were clearly detected with the pin Hard X-ray Detector up to several tens of keV, allowing for a fairly good characterization of the…
A fraction of active galactic nuclei do not show the classical Seyfert-type signatures in their optical spectra, i.e. they are optically "elusive". X-ray observations are an optimal tool to identify this class of objects. We combine new…
Chandra observations of 17 nearby galaxies were analysed and 166 bright sources with X-ray counts > 100, were chosen for temporal analysis. Fractional root mean square variability amplitudes were estimated for lightcurves binned at ~ 4 ksec…
We study the X-ray spectra of a sample of 19 obscured, optically-selected Seyfert galaxies (Sy 1.8, 1.9 and 2) in the local universe ($d \leq 175$~Mpc), drawn from the CfA Seyfert sample. Our analysis is driven by the high sensitivity of…
We present the first result of a programme to search for large flux variations in the X-ray sources of the XMM Serendipitous Survey compared to previous ROSAT observations. An increase in X-ray flux by a factor >10 was discovered from the…