Book contents
- Frontmatter
- Contents
- Index of Participants
- Preface
- I Evidence and Implications of Anisotropy in AGN
- II Luminosity Functions and Continuum Energy Distributions
- Radio Luminosity Functions of Active Galaxies
- The Quasar Luminosity Function
- UK ROSAT Deep & Extended Deep Surveys
- Luminosity Dependence of Optical Activity in Radio Galaxies
- Modelling the Quasar Luminosity Function in Hierarchical Models for Structure Formation
- Active Galactic Nuclei in Clusters of Galaxies
- Clustering Properties of AGNs and their Contribution to the X-ray Background
- Energy Distributions of AGN
- Absorption in the ROSAT X-ray Spectra of Quasars
- Dust in AGNs
- First Simultaneous UBVRI Photopolarimetric Observations of a Sample of Normal Quasars
- Intermediate Resolution Spectropolarimetry of Three Quasars
- Active Galaxies which Emit Strongly at 25μm
- III The Broad Line Region: Variability and Structure
- IV X-rays and Accretion Disks
- V Beams, Jets and Blazars
- VI Concluding Talk
Absorption in the ROSAT X-ray Spectra of Quasars
from II - Luminosity Functions and Continuum Energy Distributions
Published online by Cambridge University Press: 04 August 2010
- Frontmatter
- Contents
- Index of Participants
- Preface
- I Evidence and Implications of Anisotropy in AGN
- II Luminosity Functions and Continuum Energy Distributions
- Radio Luminosity Functions of Active Galaxies
- The Quasar Luminosity Function
- UK ROSAT Deep & Extended Deep Surveys
- Luminosity Dependence of Optical Activity in Radio Galaxies
- Modelling the Quasar Luminosity Function in Hierarchical Models for Structure Formation
- Active Galactic Nuclei in Clusters of Galaxies
- Clustering Properties of AGNs and their Contribution to the X-ray Background
- Energy Distributions of AGN
- Absorption in the ROSAT X-ray Spectra of Quasars
- Dust in AGNs
- First Simultaneous UBVRI Photopolarimetric Observations of a Sample of Normal Quasars
- Intermediate Resolution Spectropolarimetry of Three Quasars
- Active Galaxies which Emit Strongly at 25μm
- III The Broad Line Region: Variability and Structure
- IV X-rays and Accretion Disks
- V Beams, Jets and Blazars
- VI Concluding Talk
Summary
Abstract
The first ROSAT X-ray spectra of two high-redshift quasars reveal unexpectedly strong absorption when compared with similar luminosity objects at lowredshift. A third quasar shows none. A fourth, low-redshift, radio-loud quasar (3C351) with extended radio structure, shows absorption possibly due to a warm absorber with a strong OVII absorption edge.
Introduction
X-ray spectral observations of quasars have been confined to low redshift objects (z≤0.5) whose proximity makes them bright enough to study and also to those with relatively bright X-ray flux (αox≲1.5). ROSAT, with its high sensitivity, enables us to observe the spectra of high redshift (z>2) and large αox quasars for the first time. We have begun a ROSAT observing program to study the X-ray spectra of quasars selected to cover the full range of continuum properties. In particular this sample includes objects at high redshift, with relatively faint X-ray flux and with a full range of radio properties: strong, weak, extended and compact. We are also carrying out a follow-up observing program to obtain multi-wavelength (infrared – ultra-violet) data for all our ROSAT-observed quasars.
Sampling the full quasar population with ROSAT
To date we have received and analysed data for > 25 quasars. Their spectra are generally steeper than those seen at higher (e.g. Einstein IPC) energies, as observed in general with ROSAT. Our current sample includes 4 high-redshift (z>2.8) quasars with sufficient counts (> 350) to obtain spectral information (Table 1).
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- Information
- The Nature of Compact Objects in Active Galactic NucleiProceedings of the 33rd Herstmonceux Conference, held in Cambridge, July 6-22, 1992, pp. 139 - 142Publisher: Cambridge University PressPrint publication year: 1994