Engineering topics

Wang, Qingde

Publications and source records attributed to Wang, Qingde.

7 records

NASA NTRS1993

X-ray spectra of 12 distant clusters of galaxies

An X-ray spectral analysis of 12 distant clusters of galaxies observed on-axis with the Einstein Observatory imaging proportional counter is presented. Statistically, X-ray spectral data of the highest red shift clusters in the sample are inconsistent with an optically thin plasma emission model plus absorptions only in the Milky Way. Inclusions of excess absorptions in the clusters significantly improve the spectral fits to the data, indicating the possible presence of large amounts of X-ray absorbing cool gas in some of the distant clusters. By using X-ray luminosities determined from observed fluxes only in the 0.8-3.5 keV band and the temperature-to-luminosity correlation for nearby clusters, the estimated temperatures of the hot intracluster medium in these distant clusters constrain the absorption columns in the clusters. The data also show possible positive temperature evolution of the hot ICM with time which, if present, would further increase the absorptions required in fitting the spectra.

Wang, Qingde↗

NASA NTRS1993

The detection of large amounts of cool, x ray absorbing gas in distant clusters of galaxies. What does this mean?

We present an x-ray spectral study of 12 distant (z = 0.17-0.54) rich clusters of galaxies observed with the Einstein Observatory Imaging Proportional Counter. These x-ray spectral data show evidence for substantial excess absorptions beyond those expected in the galaxy, indicating the presence of large amounts of x-ray absorbing cool gas in these distant clusters. The mean value of the excess absorptions corresponds to an absorbing gas column density approximately greater than 10(exp 21)/sq cm. We calculate the x-ray luminosities of the clusters with observed fluxes only in the 0.8-3.5 keV band where the fluxes are less effected by the absorptions, and use the temperature-to-luminosity correlation (known only for nearby clusters) to estimate the temperatures of the hot intracluster medium (ICM) in the distant clusters. These temperature estimates, together with the spectral fits, provide further constraints on the column densities in the individual clusters. For the cluster CL 0016+16, the lower limit on the column density is found to be 8 x 10(exp 20)/sq cm at the 99 percent confidence limit. We also show that the ratio of the temperature obtained from the spectral fit to the temperature expected from the correlation tends to decrease with increasing look-back time, indicating possible temperature evolution of the hot ICM in the recent past. The inclusion of this evolutionary effect further increases the absorptions required in fitting the spectra.

Wang, Qingde↗

NASA NTRS1992

The BL Lacertae object PKS 1413 + 135 - Is it within or behind a spiral galaxy?

New observations of the very red quasar or BL Lac object PKS 1413 + 135 are presented. Optical imaging and spectroscopy confirm the claim that the host galaxy to this BL Lac is a spiral, and H-band imaging shows the point source centered in the galaxy to within 0.1 arcsec. A reanalysis of Einstein X-ray data finds evidence for an extremely large column density in this source. While the astrometric evidence supports the hypothesis that PKS 1413 + 135 is the very unusual case of a BL Lac object in a spiral galaxy, a highly extincted nuclear source would produce other observable features in this galaxy that are not observed: narrow emission-line region and large thermal IR flux. Their absence argues for this source being background to the spiral.

Stocke, John T.↗

NASA NTRS1992

An imaging study of the Galactic diffuse soft X-ray background

A study is performed of the Galactic diffuse soft X-ray background with the data collected with the imaging proportional counter (IPC) on board the Einstein X-ray Observatory. It is demonstrated that the IPC imaging data can provide important information on the nature of the background and significant constraints on the physical properties of the hot ISM component. The estimated pressure and density in the coronal gas are consistent with both theoretical arguments and UV observations made with IUE, HST, and rocket tests.

Wang, Qingde↗

NASA NTRS1992

A deep image of the diffuse soft X-ray background at the Galactic plane

A deep Einstein IPC image of the Galactic plane provides important information about the Galactic diffuse X-ray background. Free from contamination by sources with fluxes greater than about 4 x 10 exp -14 ergs/sq cm s and by X-rays from beyond the Galactic plane, the intensity and spectrum of the background at the Galactic plane are measured for the first time in the 0.16-3.5 keV band. The spectrum can be characterized by a thermal hot gas model with a temperature of about 4,000,000 K, and the M-band Galactic flux is about 3 x 10 exp -8 ergs/sq cm s sr. This background is enhanced in the M band at the Galactic plane, but it is keV regime. If discrete sources are to be responsible for the background, their surface density must be much greater than one source per resolution element of the IPC (i.e., about 0.4 sources/sq arcmin) because of the lack of a correlation among observed X-ray on scales comparable to the instrument resolution. This density constraint, together with a model study of the Galactic emission, leads to the conclusion that no known stellar population could be responsible for the bulk of the emission.

Wang, Qingde↗

NASA NTRS1992

A comprehensive X-ray study of the Small Magellanic Cloud

A comprehensive analysis of the Einstein data base on the SMC is presented. Twenty-four soures are classified as objects in the SMC, and 13 as Galactic stars, AGN, and clusters of galaxies. The detected discrete emitters account for less than half of the excess emission associated with the SMC. The extensive diffuse emission has an X-ray spectrum substantially softer than that of the discrete sources, which is consistent with the presence of X-ray-emitting coronal gas associated with the SMC. A detailed study of the discrete sources is presented. An X-ray source is found to vary in its X-ray luminosity by a factor larger than 10 over a period of about 1 yr and has a relatively hard X-ray spectrum which apparently changes with the X-ray luminosity. It is suggested that this source, associated with a B1-type star, is a new high-mass X-ray binary in the Small Cloud.

Wang, Qingde↗

NASA NTRS1991

N67 as an X-ray bright planetary nebula in the Small Magellanic Cloud

Among the known planetary nebulae in the SMC, N67 has the hottest nucleus and highest N/O abundance ratio. Here, the identification of this planetary with an X-ray source 1E00056.8 - 7154 is reported, and it is shown that the observed extreme soft spectrum and strong emission of this X-ray source are consistent with the radiation from the surface of a single nucleus of N67 which is collapsing into a white dwarf. At a known distance in the SMC, N67 will be invaluable in testing the understanding of the structure and evolution of planetary nebulae.

Wang, Qingde↗