Engineering topics

Mushotzky, R. F.

Publications and source records attributed to Mushotzky, R. F..

At least 73 records · Page 4

NASA NTRS1990

X-ray study of superclusters

The Batuski-Burns list of candidate superclusters was searched for X-ray emission in the HEAO 1 A-2 data base. No significant flux in excess of integrated member cluster emission was detected in directions associated with estimated supercluster centroids; a 3 sigma upper limit to the mean individual excess flux is 5 x 10 to the -12th ergs/sq cm/s. Implications of this bound are discussed in terms of fainter member clusters, hot diffuse gas, and active and normal galaxies. Prospects of supercluster observations related to future X-ray missions are also outlined.

Persic, M.↗

NASA NTRS1989

The complex X ray spectra of AGN

X-ray spectral surveys of large samples of Seyfert galaxies are discussed. The spectral shape in the 0.1 to 20 keV energy range is considered. Two new spectral survey are undertaken, one involving 105 Imaging Proportional Counter (IPC) observations of 75 Seyfert galaxies, the other using IPC and Monitor Proportional Counter (MPC) data from 28 observations of 23 Seyfert galaxies. The X-ray spectra of active galactic nuclei (AGN) are complex, with in most cases considerable steepening at the lowest energies. At higher energies (2 to 20 keV), the existence of a universal, canonical power law is confirmed, independent of X-ray luminosity over four orders of magnitude.

Urry, C. M.↗

NASA NTRS1989

Signposts to the future

The major scientific issues raised in this meeting about Active Galactic Nuclei (AGN) are summarized. The X-ray background and the capabilities of missions to be launched in the next 5 years (GRANAT, ROSAT, BBXRT, GRO, Astro-D, SAX, Spectrum-X-gamma, XTE) are discussed. Each one of these missions is considerably more powerful than its predecessor and will add to the knowledge of AGN and the X-ray background. By the end of the 1990's both of the X-ray astronomy Great Observatories, Advanced X-ray Astrophysics Facility (AXAF) and X-ray Multi mirror Mission (XMM), should be flying, each one of them more powerful than the intermediate scale missions of the early 1990's.

Mushotzky, R. F.↗

NASA NTRS1989

Einstein SSS+MPC observations of Seyfert type galaxies

The X-ray spectra of 27 Seyfert galaxies measured with the Solid State Spectrometer (SSS) onboard the Einstein Observatory is investigated. This new investigation features the utilization of simultaneous data from the Monitor Proportional Counter (MPC) and automatic correction for systematic effects in the SSS. The new results are that the best-fit single power law indices agree with those previously reported, but that soft excesses are inferred for at least 20 percent of the measured spectra. The soft excesses are consistent with either an approximately 0.25 keV black body or Fe-L line emission.

Holt, S. S.↗

NASA NTRS1989

On the ratio of the infrared-to-ultraviolet continuum to the X-rays in quasars and active galaxies

A sample of 122 quasars and Seyfert galaxies was analyzed and it was found that the NIR 7500 A rest frame luminosity is more linearly related to the X-ray luminosity than is the optical luminosity. It is also found that the mean spectral slope between 7500 and 4200 A in the rest frame monotonically flattens with luminosity over more than three orders of magnitude. The present results support models which attribute the IR and X-ray continua to linked nonthermal processes such as synchrotron self-Compton, while the blue-UV bump comes from a different source, such as an accretion disk.

Mushotzky, R. F.↗

NASA NTRS1988

Einstein Observatory solid state detector observations of cooling flows in clusters of galaxies

Einstein Observatory (EO) solid state spectrometer results for the cooling flows in nine clusters of galaxies are discussed. An analysis of the data using three separate models provides strong evidence for the existence of cool components in the centers of these clusters. The obtained distribution of emission versus temperature for M87 is found to agree well with that determined from data obtained by the EO focal Plane Crystal Spectrometer.

Mushotzky, R. F.↗

NASA NTRS1987

X-ray observations of the Ophiuchus, PKS 0745-191 and Cygnus-A clusters of galaxies

Observations are reported of the X-ray emission from three bright clusters of galaxies at low Galactic latitudes: the Ophiuchus, PKS 0745-191, and Cygnus-A clusters. Temperatures and iron abundances are determined from Exosat spectral data. Images of the Ophiuchus cluster show it to have a high central density and a cooling flow. Measurements of a high gas density around PKS 0745-191 and are confirmed, and it is shown that the X-ray emission is centered on the radio galaxy. The PKS 0745-191 cluster is the most distant object for which an abundance has been measured from X-ray spectra. The spectrum of Cygnus-A contains a highly absorbed power-law component that is identified with the nucleus of the radio source.

Arnaud, K. A.↗

NASA NTRS1986

Observational determination of the masses of active galactic nuclei

The masses of 24 active galactic nuclei are determined on the basis of published observations, using data on both the X-ray variability and the width of the narrow forbidden lines of O III. The results are presented in tables and graphs, and it is found that the mass estimates based on the X-ray variability are in good agreement with the dynamic masses determined from the O III linewidth when reasonable values are selected for the radius of the region of X-ray origin and when a standard photoionization model is adopted for the line-emitting gas. The O III dynamic masses of Seyfert-2 nuclei are shown to be systematically lower than those predicted by the (delta t)/M(O III) correlation for Seyfert-1 nuclei.

Wandel, A.↗

NASA NTRS1986

The detection of distant cooling flows and the formation of dark matter

Cooling flows involving substantial mass inflow rates appear to be common in many nearby rich and poor clusters and in isolated galaxies. The extensive optical and ultraviolet filaments produced by the thermal instability of large flows are detectable out to redshifts greater than 1. It is proposed that this may explain the extended optical line emission reported in, and around, many distant radio galaxies, narrow-line quasars, and even nearby normal and active galaxies. An important diagnostic to distinguish cooling flows from other possible origins of emission line filaments is the presence of extensive regions at high thermal pressure. Other evidence for distant cooling flows and the resultant star formation is further discussed, together with the implications of cooling flow initial-mass functions for galaxy formation and the nature of 'dark' matter.

Fabian, A. C.↗

NASA NTRS1986

X-ray spectroscopy of five BL Lacertae objects

Five X-ray bright BL Lacertae objects were observed in the energy range 0.6-4.5 keV with the solid state spectrometer (SSS) of the Einstein Observatory. The 14 SSS spectra obtained represent most of the X-ray spectra of BL Lac objects with resolution better than approximately 3. These data do not reveal the presence of large amounts of thermal gas, with upper limits for the equivalent width of individual spectral features typically less that about 100 eV. However, the SSS spectra are the first set of X-ray data to indicate low-energy absorption in excess of that caused by the cold interstellar matter in the Galaxy. Comparison with contemporaneous, lower energy X-ray data implies that this absorption does not arise in cold neutral material, but in hotter, highly ionized material, probably intrinsic to the source. All five BL Lac objects have X-ray continua that are well fitted by power-law models, with power-law energy indices usually greater than about 1. In a few cases, a flattening at higher energies is observed; these and other data suggest that two-component X-ray spectra, steep at low energies and flat at high energies, are a common feature of BL Lac objects. Three of the five sources clearly vary between SSS observations, with time scales ranging from days to years. A historical synopsis of the X-ray spectral data confirms the tendency for BL Lacertae objects to be highly variable in the X-ray band but reveals no correlation between spectral and intensity changes.

Urry, C. M.↗

NASA NTRS1986

Limits of X-ray variability in active galactic nuclei

A significant correlation is demonstrataed here between the X-ray luminosity and the timescale of X-ray variability for Seyfert galaxies and quasars. This is interpreted as evidence that the emitting plasma is near the limit of being dominated by electron-positron pairs. BL Lac objects do not follow this pattern; this may be due either to relativistic beaming or to the differing importance of the pair production process.

Barr, P.↗

NASA NTRS1986

X-ray absorption in active galaxies - Constraints on the broad-line emitting regions

X-ray observations of intrinsic absorption in active galactic nuclei (AGN) provide direct information concerning the amount and physical properties of cool (unionized) material along the line of sight. The X-ray absorption is assumed to occur in the broad-line emitting gas, so that the X-ray data can be used to probe the conditions in the broad-line regions of AGN. The results of Einstein Observatory solid state spectrometer observations are used to derive detailed physical constraints concerning the geometry of the broad-line region. Physical implications of these constraints are also discussed.

Reichert, G. A.↗

NASA NTRS1986

The X-ray spectrm of the Coma Cluster of galaxies

The HEAO 1 A-2 and OSO 8 observations of the Coma Cluster of galaxies in the 2-60 keV energy band are presented. The spectrum is not well fitted by an isothermal bremsstrahlung model with an Fe line. To model the spectrum more accurately, we have performed fits of polytropic models and find that the gas is well fitted by an equation of state with polytropic index ranging between 1.38 and 1.6. This analysis reduces the total cluster mass by a factor of 3-5 below the optically derived virial mass. Using the best-fitting parameters, the gas is found to be a significant fraction (25 percent) of the total cluster mass. The Fe K-alpha line blend is strongly detected, from which we infer 0.18-0.36 solar abundance in the X-ray emitting gas. The Fe K-beta line blend is also weakly detected. The spectrum is not consistent with the existence of a hard X-ray tail at the flux level reported by Bazzano el al. (1984). In addition, the HEAO I scanning mode data place strong constraints on possible contaminating sources in the region surrounding Coma.

Henriksen, M. J.↗

NASA NTRS1986

The GSFC/Wisconsin X-ray spectroscopy investigation for AXAF

A novel device is described which combines the high quantum efficiency of a photoelectric detector with the high energy resolution of a dispersive spectrometer in a system that operates simultaneously over the whole AXAF bandpass. It is basically an X-ray calorimeter, in which the temperature rise of an X-ray absorber following the deposition of energy from a single X-ray photon can be measured to an accuracy expected to be of order one part in 1000 at 6 keV.

Holt, S. S.↗

NASA NTRS1985

An X-ray, optical and radio study of PKS 0745-191 - A massive cooling flow

The X-ray source 3A 0745-191 is identified with intracluster gas surrounding the giant galaxy containing the radio source, PKS 0745-191, which lies at z = 0.1. The gas is cooling at the unprecedented rate of 1000 solar mass/yr. Optical line-emitting gas extends more than 10 kpc from the centre of the galaxy and corroborates the high mass-flow rate. The optical spectrum is similar to that of distant 3CR radio galaxies reported by others. It is concluded that formation of a giant galaxy was observed.

Fabian, A. C.↗

NASA NTRS1985

Soft X-ray spectral observations of low-luminosity active galaxies

The X-ray spectra of a sample of 12 low-luminosity AGNs observed using the solid state spectrometer on the HEAO 2 satellite are investigated. The AGNs discussed here have X-ray luminosities below about 10 to the 44th erg/s, and thus form a sample complementary to the higher luminosity sample discussed by Petre et al. (1984). The spectra are well described by a simple model consisting of a power law, with photon spectral index about 1.7, plus absorption by cold gas. The objects in the sample can be separated into three groups: (1) those whose spectra show no significant absorption; (2) those for which the X-ray source is totally covered by a spatially uniform absorbing medium; and (3) those for which partial covering by 'patchy' absorbers is indicated. Column densities and covered fractions do not correlate systematically with X-ray luminosity. Implications regarding physical conditions in AGNs are discussed.

Reichert, G. A.↗

NASA NTRS1985

The physical implications of an isothermal model for the hot intracluster medium

HEAO-1 A-2 and Einstein Observatory IPC observations of 15 clusters of galaxies have been used to measure the isothermal beta-model parameters, and the parameters are compared with those derived from model fits to the X-ray images. The physical constraints imposed on this model by existing optical data, the implied gas mass, and the gas contribution to the binding cluster mass are addressed. Values of beta less than unity are obtained, consistent with results from X-ray imaging data. This is interpreted to imply that the gas extends out to 8-10 core radii, about 2-3 Mpc. The isothermal gas mass can be as large as 60 percent of the virial mass for some clusters. This contradicts the fundamental assumption that the cluster potential is determined by an unseen mass which is given by the King approximation to an isothermal sphere, and it is concluded that the isothermal model is a nonphysical model.

Henriksen, M. J.↗

NASA NTRS1985

Spectral constraints on models of gas in clusters of galaxies

The HEAO 1A2 spectra of clusters of galaxies are used to determine the temperature profile which characterizes the X-ray emitting gas. Strong evidence of nonisothermality is found for the Coma, A85, and A1795 clusters. Properties of the cluster potential which binds the gas are calculated for a range of model parameters. The typical binding mass, if the gas is adiabatic, is 2-4E14 solar masses and is quite centrally concentrated. In addition, the Fe abundance in Coma is .26 + or - .06 solar, less than the typical value (.5) found for rich clusters. The results for the gas in Coma may imply a physical description of the cluster which is quite different from what was previously believed.

Henriksen, M. J.↗