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Ku, W. H.-M.

Publications and source records attributed to Ku, W. H.-M..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Imaging X-ray spectrophotometric observation of SN 1006

An imaging gas scintillation proportional counter (IGSPC) at the focal plane of a grazing incidence telescope was carried aloft by a sounding rocket and used to observe soft X-ray emission from the supernova remnant SN 1006. The instrument obtained the first unambiguous detection of strong (8 + or 0.0-2 photons/sq cm s) oxygen He-alpha and Ly-alpha emission at 0.59 + or - 0.02 keV from SN 1006. This line emission is consistent with emission from a 1.8 x 10 to the 6th K plasma, although hard X-ray emission from an additional power law or a higher temperature component was also observed. The X-ray emission may be interpreted as due to either (1) a combination of blast-wave and reverse shock assuming equilibrium ionization in the plasma or (2) blast-wave emission alone with a significant degree of ionization disequilibrium.

Vartanian, M. H.↗
NASA NTRS1984

Two multifrequency observations of 3C 371

Observations of 3C371 made at frequencies from the radio to the ultraviolet and coordinated during two short time intervals separated by 3 months are presented. Also presented are 1 keV X-ray flux densities measured at a different time. The multifrequency measurements indicate spectral steepening at visual wavelengths, and that an extrapolation of the ultraviolet continuum falls below the X-ray data. The infrared through X-ray data is explained as relativistically beamed synchrotron self-Compton emission, and source parameters are derived for two possible models. The present ultraviolet spectra both show strong Lyman-alpha emission at the same redshift as weak optical emission lines reported previously. Production of these lines by recombination of gas, after its ionization by the ultraviolet to X-ray continuum radiation, is favored as an explanation. C IV and N V absorption lines are tentatively identified in one ultraviolet spectrum, which, if real, suggest the presence of a hot (about 300,000 K) gaseous halo in 3C 371.

Puschell, J. J.↗
NASA NTRS1984

Einstein Observations of the Cygnus Loop

The imaging instruments on the Einstein Observatory were used to study the detailed X-ray structure of the Cygnus Loop. An arc minute resolution map of the 0.1-4.0 keV emission from the entire remnant was obtained with the imaging proportional counter (IPC). The bright northeastern and western limbs were mapped with the high resolution imager (HRI). The large-scale structure of the Loop is well modeled as a limb-brightened shell of hot gas at 2 x 10 to the 6th K created by the expansion of a blast wave into an inhomogeneous interstellar medium. The pulse-height data from the IPC indicate that the center of the remnant is generally hotter than the limb with temperatures as high as 4 x 10 to the 6th K. The X-ray maps show good general correlation with large-scale radio and optical structure, and in some cases good detailed correlation with faint optical filaments dominated by hydrogen line emission.

Ku, W. H.-M.↗
NASA NTRS1984

A large area imaging gas scintillation proportional counter for use in X-ray astronomy

A large area (200 sq cm), broad bandwidth (0.1-70 keV), imaging gas scintillation proportional counter (IGSPC) has been constructed for use in X-ray astronomy. The IGSPC consists of a high pressure xenon gas scintillation proportional counter (GSPC) coupled to a multi-wire proportional counter (MWPC) via a calcium fluoride window. THe MWPC, filled with a mixture of argon, methane, and tetrakis (dimethylamino) ethylene, detects the UV photons emitted by the xenon gas in the GSPC. The detector has a measured energy resolution of 8.0 percent (FWHM) and 4.3 percent (FWHM) at 5.9 keV and 22.1 keV, respectively. The predicted spatial resolution of the detector is less than 1 mm (FWHM) between 3-22 keV and 37-60 keV. A method to determine the three-dimensional location of detected X-rays is described. In addition, a combination of discrimination schemes designed to reduce the non-X-ray background in the IGSPC by more than two orders of magnitude is discussed.

Ku, W. H.-M.↗
NASA NTRS1983

Six quasars near the jets of NGC 1097

Six quasars have been discovered in a 0.43 sq deg field surrounding NGC 1097. The quasars are grouped in a small area of the field: five of the quasars lie within the area defined by the jets emanating from the galaxy. Four of the quasars are clearly detected in a deep X-ray map of the field. The probability of finding such an unusual configuration is discussed.

Wolstencroft, R. D.↗
NASA NTRS1983

X-rays and rotation among post-T Tauri G stars in Orion Ic

Walter and Kuhi (1981) have shown that at least 10 out of 12 T Tauri stars brighter than m(v) = 12.5 are X-ray emitters. The X-ray luminosities of these stars, L(x), are often close to the detection threshold value. One of the principal results of the present investigation is the evidence for at least a weak correlation between L(x) and V(R) sin i. If it is assumed that results obtained concerning stars in the Orion Ic Association are representative of other stellar fields, it appears that along with the RS CVn stars, pre-main-sequence G stars are among the most X-ray luminous late-type stars on the H-R diagram. A second conclusion is that the X-rays are almost certainly produced by flares and/or thin coronae close to the stellar surface.

Smith, M. A.↗
NASA NTRS1983

X-ray survey of clusters of galaxies with the Einstein Observatory

A sample of 74 clusters of galaxies from the Abell catalog has been observed with the Einstein Observatory. Fifty-three of the clusters were detected. X-ray luminosities and core radii have been measured, and possible correlations between these parameters and optical and radio cluster parameters have been examined. The results are consistent with a thermal bremsstrahlung model for the X-ray emission in which a significant fraction of the gas has been supplied by ram-pressure stripping. In addition, the X-ray luminosity function of clusters has been calculated, and it is shown that clusters contribute approximately 10 percent to the soft X-ray background in the 0.5-4.0 keV band.

Abramopoulos, F.↗
NASA NTRS1983

X-ray observations of the southern cluster CA 0340-538 and the Horologium supercluster

X-ray observations of the Horologium supercluster are examined. Results show that the optically Coma-like cluster CA 0340-538 has a smooth X-ray structure which also resembles that of Coma. The density structure of its X-ray emitting gas, determined in a model-independent way, is found to be remarkably featureless, being consistent with a nearly isothermal polytrope out to approximately 2 Mpc from the cluster center. The total mass of the gas is determined to exceed 10% of the cluster virial mass and may contribute a substantial fraction of the cluster binding mass. Although CA 0329-527 is found to be an X-ray double cluster, its structure appears to be confused. CA 0325-539 is found to show no substantial X-ray emission. An upper limit of 1.3 x 10 to the 44th erg/s is determined for any diffuse 2-10 keV emission from the Horologium supercluster.

Ku, W. H.-M.↗
NASA NTRS1983

Studies of BL Lacertae objects with the Einstein X-ray observatory - The absolute volume density

It is estimated that the local volume density of BL Lac objects which emit greater than 10 to the 44th ergs/s in the 0.5-4.5 keV band is about 10 to the -7th/cu Mpc. This is based on identifications of bright X-ray sources, and the fact that Einstein X-ray observations detect BL Lac objects over a wide, continuous range of flux up to the thresholds of the all-sky X-ray surveys. Since this density is of the same order of magnitude as the local density of Seyfert galaxies, or local density of optically selected quasars, emitting X-rays at the same luminosity, we argue that the difference between these particular astronomical classifications is not solely due to the orientation of a relativistic beam.

Schwartz, D. A.↗
NASA NTRS1983

Detalied X-ray observations of the Cygnus Loop

High quality X-ray spectra and imaging observations of the Cygnus Loop have been obtained with three different instruments. The High Resolution Imager (HRI) on the Einstein Observatory was used to obtain arcsecond resolution images of select bright regions in the Cygnus Loop which permit detailed comparisons between the X-ray, optical, and radio structure of the Loop. The Imaging Proportional Counter (IPC) on the Einstein Observatory was used to obtain an arcminute resolution map of essentially the full Loop structure. Finally, an Imaging Gas Scintillation Proportional Counter (IGSPC), carried aloft by a sounding rocket last fall, obtained modest resolution, spatially resolved spectrophotometry of the Cygnus Loop. An X-ray map of the Loop in the energy of the O VIII line was obtained. These data combine to yield a very powerful probe of the abundance, temperature, and density distribution of material in the supernova remnant, and in the interstellar medium.

Ku, W. H.-M.↗
NASA NTRS1983

An imaging gas scintillation proportional counter for use in X-ray astronomy

An imaging gas scintillation proportional counter (GSPC) has been constructed for use in X-ray astronomy. The IGSPC consists of a gas scintillation proportional counter (GSPC) with a 1 micron polypropylene window coupled to a multiwire proportional counter (MWPC) via a calcium fluoride window. The MWPC, filled with a mixture of argon, methane, and tetrakis (dimethylamino) ethylene, detects the UV photons emitted by the xenon gas in the GSPC. The measured energy resolution is 17.0 percent (fwhm) and 8.0 percent (fwhm) at 1.5 keV and 5.9 keV, respectively. The measured position resolution is 1.9 mm (fwhm) and 0.9 mm (fwhm) at 1.5 and 5.9 keV, respectively. Possible astrophysical observations which can be performed with an IGSPC at the focal plane of a grazing incidence telescope are also discussed.

Hailey, C. J.↗
NASA NTRS1982

A detailed X-ray study of the cooling intracluster gas in A496

X-ray observations of the galaxy cluster A496 are presented. Imaging and spectral data, together with the presence of optical filaments, show that radiative cooling is occurring in the cluster core and indicates a mass flow rate of about 200 solar masses per year on to the central galaxy. The gas temperature and density profiles within the core are similar to those in the Perseus cluster (A426) despite a six-fold difference in total X-ray luminosity. This is consistent with the model of Fabian and Nulsen (1977, 1979) for steady flows caused by cooling. The evolution of cooling flows is discussed and it is shown that thermal conduction is suppressed to well below the Spitzer rate.

Nulsen, P. E. J.↗
NASA NTRS1982

Simultaneous observations of the BL Lacertae object I Zw 187

Two sets of simultaneous spectra consisting of data obtained with radio, IR, optical, UV and X-ray telescopes were obtained 10 months apart for the X-ray bright BL Lac object IZw 187. In addition, nonsimultaneous observations were made in several of the aforementioned observing bands in order to detect flux variations and galactic light contamination was removed from all observations. The BL Lac component is found to have a weak 3000 A bump superposed on an IR-optical-UV spectrum of slope 0.9. Consistent with the arising of the IR-through-X-ray continuum from a single synchrotron source, the X-ray data fall on or near an extrapolation of this power law. No flux variations have been detected in the flat radio spectrum. Optical and X-ray fluxes are observed to vary by a factor not greater than three, and the shortest variability time scales in these bands are comparable at about one week.

Bregman, J. N.↗
NASA NTRS1982

For the detection of subkiloelectron-volt X-rays

A large-area, imaging gas scintillation proportional counter (IGSPC) has been constructed for use in X-ray astronomy. The IGSPC consists of a gas scintillation proportional counter (GSPC) with a 1-micron polypropylene window coupled to a multiwire proportional counter (MWPC) via a calcium fluoride window. The MWPC, filled with a mixture of argon, methane, and tetrakis (dimethylamino) ethylene, detects the UV photons emitted by the xenon gas in the GSPC. Over a sensitive area of 21 sq cm, the instrument has a measured energy resolution of 17.5% (FWHM) and 1.9 mm (FWHM) spatial resolution at 1.5 keV.

Hailey, C. J.↗
NASA NTRS1982

High-resolution X-ray observations of the Orion Nebula

Observations of the Trapezium region in the Orion Nebula have been obtained with the high-resolution X-ray imaging instrument on the Einstein Observatory. At least 58 sources of the X-ray emission have been revealed, and all but two can be identified with visible stars. The strongest source is the star theta(1)C, which excites the emission nebula, and has an X-ray luminosity of 6 x 10 to the 32nd ergs/s. No strong X-ray emission has been observed from members of the infrared cluster embedded within the Orion molecular cloud.

Ku, W. H.-M.↗
NASA NTRS1981

On the equilibrium distribution of the elements in the gas in the Coma cluster

The equilibrium distribution of the elements for the case of an isothermal plasma in a gravitational potential well is given governing equations and a rapidly converging iterative procedure for their solution. Results are applied to the intracluster gas in clusters of galaxies, and implications are identified for the controversy as to whether iron nuclei settle out in the cluster core, and with respect to the interpretation of distribution size and shape for continuum X-ray emission from clusters. A model for the Coma cluster is considered in which the intracluster gas is in equilibrium and partially processed. It is found that this model can account for the angular dependence of the continuum X-ray emission from Coma, as determined by Einstein Observatory observations, at least as well as the uniform composition model.

Abramopoulos, F.↗
NASA NTRS1981

Properties of an imaging gas scintillation proportional counter

An instrument which combines the improved energy resolution offered by the gas scintillation proportional counter (GSPC) with the submillimeter imaging capabilities of the multiwire proportional counter (MWPC) is described. The imaging gas scintillation proportional counter detects the centroid of the UV light excited by X-ray photons interacting in the noble gas of the GSPC with a UV sensitive gas in the MWPC. The prototype counter yields a measured performance of 9% (FWHM) energy resolution and 0.9 mm (FWHM) spatial resolution at 6 keV. Further design refinements should achieve 18% (FWHM) energy resolution and 0.6 mm (FWHM) spatial resolution at 1 keV.

Ku, W. H.-M.↗