We present an analysis of 16 galaxy clusters, one group, and one galaxy drawn from the Chandra Data Archive. These systems possess prominent X-ray surface brightness depressions associated with cavities or bubbles that were created by interactions between powerful radio sources and the surrounding hot gas. The central galaxies in these systems harbor radio sources with luminosities ranging between ~2 × 1038 and 7 × 1044 ergs s-1. The cavities have an average radius of ~10 kpc, and they lie at an average projected distance of ~20 kpc from the central galaxy. The minimum energy associated with the cavities ranges from pV ~ 1055 ergs in galaxies, groups, and poor clusters to pV ~ 1060 ergs in rich clusters. We evaluate the hypothesis that cooling in the hot gas can be quenched by energy injected into the surrounding gas by the rising bubbles. We find that the instantaneous mechanical luminosities required to offset cooling range between 1pV and 20pV per cavity. Nearly half of the systems in this study may have instantaneous mechanical luminosities large enough to balance cooling, at least for a short period of time, if the cavities are filled with a relativistic gas. We find a trend or upper envelope in the distribution of central X-ray luminosity versus instantaneous mechanical luminosity, with the sense that the most powerful cavities are found in the most X-ray-luminous systems. Such a trend would be expected if many of these systems produce bubbles at a rate that scales in proportion to the cooling rate of the surrounding gas. Finally, we use the X-ray cavities to measure the mechanical power of radio sources over six decades of radio luminosity, independently of the radio properties themselves. We find that the ratio of the instantaneous mechanical (kinetic) luminosity to the 1.4 GHz synchrotron luminosity ranges typically between a few and roughly a few thousand for luminous radio sources but can be several thousand for weaker sources. This wide range implies that the 1.4 GHz synchrotron luminosity is an unreliable gauge of the mechanical power of radio sources.

/pdf/a-systematic-study-of-radio-induced-x-ray-cavities-in-3ipbzlxe30.pdf

A Systematic Study of Radio-induced X-Ray Cavities in Clusters, Groups, and Galaxies

We present the results from a detailed analysis of the 0.6-10 keV spectra of 23 ASCA observations of 18 objects. We find that in most cases the underlying continuum can be well represented by a power law with a photon index Γ ~ 2. However, we find strong evidence for photoionized gas in the line of sight to 13/18 objects. We present detailed modeling of this gas based upon the ION photoionization code. Other studies have been made of the "warm absorber" phenomenon, but this paper contains the first consideration of the importance of the covering fraction of the ionized gas and a direct comparison between models of attenuation by ionized versus neutral material. We find the X-ray ionization parameter for the ionized material is strongly peaked at UX ~ 0.1. The column densities of ionized material are typically in the range NH, z ~ 1021-1023 cm-2, although highly ionized (and hence pseudotransparent) column densities up to 1024 cm-2 cannot be excluded in some cases. We also investigate the importance of the emission spectrum from the ionized gas, finding that it significantly improves the fit to many sources with an intensity consistent with material subtending a large solid angle at the central source. Allowing a fraction of the continuum to be observed without attenuation also improves the fit to many sources and is definitely required in the case of NGC 4151. A deficit of counts is observed at ~1 keV in the sources exhibiting the strongest absorption features. We suggest this is likely to be the signature of a second zone of (more highly) ionized gas, which might have been seen previously in the deep Fe K-shell edges observed in some Ginga observations. We find evidence that the ionized material in NGC 3227 and MCG -6-30-15 contains embedded dust, while there is no such evidence in the other sources We discuss these results in the context of previous studies and briefly explore the implications in other wave bands.

ASCA Observations of Seyfert 1 Galaxies. III. The Evidence for Absorption and Emission Due to Photoionized Gas

The High Energy X-Ray Timing Experiment (HEXTE) is one of three scientific instruments aboard the Rossi X-Ray Timing Explorer (RXTE), which was launched on 1995 December 30. RXTE performs timing and spectral studies of bright X-ray sources to determine the physical parameters of these systems. The HEXTE consists of two independent clusters of detectors, each cluster containing four NaI(Tl)/CsI(Na) phoswich scintillation counters sharing a common 1° FWHM field of view. The field of view of each cluster is switched on and off source to provide near real-time background measurements. The net open area of the eight detectors is 1600 cm2, and each detector covers the energy range 15-250 keV with an average energy resolution of 15.4% at 60 keV. The in-flight performance of the HEXTE is described, the light curve and spectrum of the Crab Nebula/pulsar is given, and the 15-240 keV spectrum of the weak source, active galaxy MCG +8-11-11 is presented to demonstrate the weak source spectral capabilities of HEXTE.

http://iopscience.iop.org/article/10.1086/305377/pdf

In-Flight Performance of the High Energy X-Ray Timing Experiment on the Rossi X-Ray Timing Explorer

We present ASCA spatial, temporal, and spectral data for a sample of 26 observations of 25 type 2 active galactic nuclei (AGNs), composed of 17 Seyfert 2 galaxies and eight narrow emission line galaxies (NELGs). Twenty-four of the 25 sources were detected. The ASCA images are generally consistent with emission from point sources at energies above ~3 keV. We use archival ROSAT data to examine each field at high spatial resolution and to check for the presence of sources that would contaminate the ASCA data. Of the five sources bright enough for 128 s temporal analysis, three are variable at >99% confidence, with characteristics consistent with those observed in Seyfert 1 galaxies. Analysis on a timescale of 5760 s reveals six sources variable at >99% confidence, and comparison with previous X-ray results shows most of the sample to be variable in hard X-ray flux on timescales of years. Simple continuum models are fitted to the sample spectra to characterize the variety of spectral forms and hence to determine the fundamental nature of the X-ray spectrum of each source. No single spectral model provides an adequate fit to all the sample sources. Thirty-six percent of the sample cannot be adequately fitted by any of our test models (all rejected at >95% confidence). Approximately half of the sample have an iron Kα line with an equivalent width consistent with an origin in the line-of-sight absorber; the remaining lines must be produced in material out of the line of sight. Absorbing columns up to 1024 atoms cm-2 are detected, and even larger columns are inferred for some sources. The mean underlying hard X-ray power-law index is Γ ~ 2. Many X-ray emission lines were detected at high levels of confidence. The iron K-shell regime is dominated by emission from neutral material. Many data sets also show evidence for complexity in the iron Kα profile, which may be interpreted as evidence for broad-line profiles, including flux both redward and blueward of the line peak, and/or for the existence of hydrogen-like and helium-like iron K lines. Hydrogen-like and helium-like lines are detected from Fe, Ne, Si, S, and Ar in addition to Mg lines. While almost half of the sample have an estimated starburst contribution of >30% in the 0.5-4.5 keV bandpass, the soft X-ray emission lines are not solely associated with a strong starburst component.

ASCA Observations of Type 2 Seyfert Galaxies. I. Data Analysis Results

THE evidence accumulated over the past few years for strong soft X-ray emission from active galactic nuclei1–3 has been interpreted as black body emission from the innermost stable region of an accretion disk feeding the putative black hole at the centre of the active nucleus, a view given strong support by the rapid variability of some soft X-ray components4. More recently, new X-ray data from the Exosat and Ginga satellites have revealed a second indicator of optically thick matter in the vicinity of the active nucleus, in the form of an iron K-fluorescence line at ≈6.4 keV (refs 5–8). We report the discovery of two further common features of continuum absorption and reflection, revealed in a composite spectrum from twelve Ginga observations of Seyfert-type active galactic nuclei. Most of these spectral features are shown to be well modelled by reprocessing of the hard X-ray power-law continuum in a slab (or perhaps a disk) of cold matter. There is also evidence for a substantial line-of-sight column of photoionized material.

X-ray reflection from cold matter in the nuclei of active galaxies

/pdf/seyfert-galaxies-as-x-ray-sources-4458omvcab.pdf

Seyfert galaxies as X-ray sources

Detection of X-ray emission from the giant radio lobes of Cen A

Four emission line galaxies, NGC 1365, 2992, 5506 and 7582, previously recognized as X-ray emitters in the range 1042–1043 erg/sec, have been observed with the Einstein Observatory Imaging Proportional Counter (IPC), in one case (NGC 2992) also with the High Resolution Imager (HRI). The Monitor Proportional Counter (MPG) data collected during these and other (courtesy S. Holt and R. Mushotzky) observations represent an important complement. This note summarizes the results and the discussion presented in two papers, Maccacaro and Perola (1981), Maccacaro, Perola and Elvis (1981).

G. C. Perola

Papers

Seyfert galaxies as X-ray sources

Detection of X-ray emission from the giant radio lobes of Cen A

X-Ray Observations of Emission Line Galaxies with the Einstein Observatory