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Forman, W.

Publications and source records attributed to Forman, W..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

High-resolution X-ray observations of the central region of M31 with the Rosat satellite

A 48,000-sec observation of M31's central 34 arcmin, using the Rosat HRI, has led to the detection of 86 X-ray sources with luminosities above 1.4 x 10 exp 36 ergs/sec; of these, 18 sources are identified with globular clusters and two with SNRs. An extrapolation of the cumulative luminosity distribution to fainter luminosities indicates that only about 15-26 percent of the diffuse X-ray emission in the bulge is attributable to faint unresolved sources from this distribution. The spatial distribution and number density of X-ray sources in M31 appear to be very different from those of our Galaxy.

Primini, F. A.↗
NASA NTRS1993

Discovery of a new component in the gravitationally lensed quasar 0957 + 561

X-ray observations of the gravitationally lensed quasar 0957 + 561 with the Einstein Observatory High Resolution Imager indicate the presence of a new component in the system. The significantly greater X-ray intensity of image A compared with image B and the extended X-ray emission can be interpreted as the gravitational lensing of a quasi-circular X-ray emitting region into a partial Einstein ring. It is suggested that the observed X-ray emission is produced by a strong cooling flow which could arise were 0957 + 561 embedded in a group of cluster galaxies.

Jones, C.↗
NASA NTRS1993

The Einstein Observatory catalog of IPC x ray sources. Volume 4E: Right ascension range 08h 00m to 11h 59m

The Einstein Observatory (HEAO-2, launched November 13, 1978) achieved radically improved sensitivity over previous x-ray missions through the use of focusing optics which simultaneously afforded greatly reduced background and produced true images. During its 2.5-yr mission, the Einstein X-Ray Telescope was pointed toward some 5,000 celestial targets, most of which were detected, and discovered several thousand additional 'serendipitous' sources in the observed fields. This catalog contains contour diagrams and source data, obtained with the imaging proportional counter in the 0.16 to 3.5 keV energy band, and describes methods for recovering upper limits for any sky position within the observed images, The main catalog consists of six volumes (numbered 2 through 7) of right ascension ordered pages, each containing data for one observation. Along with the primary documentaion describing how the catalog was constructed, volume 1 contains a complete source list, results for merged fields, a reference system to published papers, and data useful for calculating upper limits and fluxes.

Harris, D. E.↗
NASA NTRS1993

The Einstein Observatory catalog of IPC x ray sources. Volume 5E: Right ascension range 12h 00m to 15h 59m

The Einstein Observatory (HEAO-2, launched November 13, 1978) achieved radically improved sensitivity over previous x-ray missions through the use of focusing optics, which simultaneously afforded greatly reduced background and produced true images. During its 2.5-yr mission, the Einstein X-Ray Telescope was pointed toward some 5,000 celestial targets, most of which were detected, and discovered several thousand additional 'serendipitous' sources in the observed fields. This catalog contains contour diagrams and source data, obtained with the imaging proportional counter in the 0.16 to 3.5 keV energy band, and describes methods for recovering upper limits for any sky position within the observed images. The main catalog consists of six volumes (numbered 2 through 7) of right ascension ordered pages, each containing data for one observation. Along with the primary documentation describing how the catalog was constructed, volume 1 contains a complete source list, results for merged fields, a reference system to published papers, and data useful for calculating upper limits and fluxes.

Harris, D. E.↗
NASA NTRS1993

The Einstein Observatory catalog of IPC x ray sources. Volume 6E: Right ascension range 16h 00m to 19h 59m

The Einstein Observatory (HEAO-2 launched November 13, 1978) achieved radically improved sensitivity over previous x-ray missions through the use of focusing optics, which simultaneously afforded greatly reduced background and produced true images. During its 2.5-yr mission, the Einstein X-Ray Telescope was pointed toward some 5,000 celestial targets, most of which were detected, and discovered several thousand additional 'serendipitous' sources in the observed fields. This catalog contains contour diagrams and source data, obtained with the imaging proportional counter in the 0.16 to 3.5 keV energy band, and describes methods for recovering upper limits for any sky position within the observed images. The main catalog consists of six volumes (numbered 2 through 7) of right ascension ordered pages, each containing data for one observation. Along with the primary documentation describing how the catalog was constructed, volume 1 contains a complete source list, results for merged fields, a reference system to published papers, and data useful for calculating upper limits and fluxes.

Harris, D. E.↗
NASA NTRS1993

The Einstein Observatory catalog of IPC x ray sources. Volume 7E: Right ascension range 20h 00m to 23h 59m

The Einstein Observatory (HEAO-2, launched November 13, 1978) achieved radically improved sensitivity over previous x-ray missions through the use of focusing optics which simultaneously afforded greatly reduced background and produced true images. During its 2.5-yr mission, the Einstein X-Ray Telescope was pointed toward some 5,000 celestial targets, most of which were detected, and discovered several thousand additional 'serendipitous' sources in the observed fields. This catalog contains contour diagrams and source data, obtained with the imaging proportional counter in the 0.16 to 3.5 keV energy band, and describes methods for recovering upper limits for any sky position within the observed images. The main catalog consists of six volumes (numbered 2 through 7) of right ascension ordered pages, each containing data for one observation. Along with the primary documentation describing how the catalog was constructed, volume 1 contains a complete source list, results for merged fields, a reference system to published papers, and data useful for calculating upper limits and fluxes.

Harris, D. E.↗
NASA NTRS1993

The Einstein Observatory catalog of IPC x ray sources. Volume 1E: Documentation

The Einstein Observatory (HEAO-2, launched November 13, 1978) achieved radically improved sensitivity over previous x-ray missions through the use of focusing optics, which simultaneously afforded greatly reduced background and produced true images. During its 2.5-yr mission, the Einstein X-Ray Telescope was pointed toward some 5,000 celestial targets, most of which were detected, and discovered several thousand additional 'serendipitous' sources in the observed fields. This catalog contains contour diagrams and source data, obtained with the imaging proportional counter in the 0.16 to 3.5 keV energy band, and describes methods for recovering upper limits for any sky position within the observed images. The main catalog consists of six volumes (numbered 2 through 7) of right ascension ordered pages, each containing data for one observation. Along with the primary documentation describing how the catalog was constructed, volume 1 contains a complete source list, results for merged fields, a reference system to published papers, and data useful for calculating upper limits and fluxes.

Harris, D. E.↗
NASA NTRS1993

The Einstein Observatory catalog of IPC x ray sources. Volume 2E: Right ascension range 00h 00m to 03h 59m

The Einstein Observatory (HEAO-2, launched November 13, 1978) achieved radically improved sensitivity over previous x-ray missions through the use of focusing optics which simultaneously afforded greatly reduced background and produced true images. During its 2.5-yr mission, the Einstein X-Ray Telescope was pointed toward some 5,000 celestial targets, most of which were detected, and discovered several thousand additional 'serendipitous' sources in the observed fields. This catalog contains contour diagrams and source data, obtained with the imaging proportional counter in the 0.16 to 3.5 keV energy band, and describes methods for recovering upper limits for any sky position within the observed images. The main catalog consists of six volumes (numbered 2 through 7) of right ascension ordered pages, each containing data for one observation. Along with the primary documentation describing how the catalog was constructed, volume 1 contains a complete source list, results for merged fields, a reference system to published papers and data useful for calculating upper limits and fluxes.

Harris, D. E.↗
NASA NTRS1993

The Einstein Observatory catalog of IPC x ray sources. Volume 3E: Right ascension range 04h 00m to 07h 59m

The Einstein Observatory (HEAO-2, launched November 13, 1978) achieved radically improved sensitivity over previous x-ray missions through the use of focusing optics which simultaneously afforded greatly reduced background and produced true images. During its 2.5-yr mission, the Einstein X-Ray Telescope was pointed toward some 5,000 celestial targets, most of which were detected, and discovered several thousand additional 'serendipitous' sources in the observed fields. This catalog contains contour diagrams and source data, obtained with the imaging proportional counter in the 0.16 to 3.5 keV energy band, and describes methods for recovering upper limits for any sky position within the observed images. The main catalog consists of six volumes (numbered 2 through 7) of right ascension ordered pages, each containing data for one observation. Along with the primary documentation describing how the catalog was constructed, volume 1 contains a complete source list, results for merged fields, a reference system to published papers and data useful for calculating upper limits and fluxes.

Harris, D. E.↗
NASA NTRS1992

Arcminute fluctuations in the microwave background from clusters of galaxies

A method for computing arcmin microwave fluctuations produced by Compton scattering of the cosmic background photons by hot electrons in clusters of galaxies is described. Microwave images of the sky for a range of Omega and primordial fluctuation spectral index n are generated which are then 'observed' to determine Delta T/T in precisely the same manner as actual observations to determine if the cluster-induced fluctuations are consistent with the measured upper limit. The geometry used by Uson and Wilkinson (1984) in the NRAO experiment and Readhead et al. (1989) in the OVRO experiment are applied to the simulated images. The 95 percent confidence lower limit for Omega is found to be about 1/10 for n = -1 (which approximates the CDM mass spectrum for clusters), while for n = 0 it is 1/7; for n = +1 the limit is 1/5 if the gas density profile extends to five core radii.

Markevitch, M.↗
NASA NTRS1992

A2163 - An exceptionally hot cluster of galaxies

The X-ray spectrum of the distant galaxy cluster A2163 was measured in the energy range 1-18 keV with the Ginga satellite. A combined analysis of these data with data previously obtained with the Einstein Observatory is presented. The mean temperature and X-ray luminosity derived are exceptionally high compared to other clusters: kT = 12.9 keV, L(x) (2-10 keV) = 3.5 x 10 exp 45 ergs/s for z = 0.15, as are the gas mass (6.7 x 10 exp 14 solar mass) and binding mass (25 x 10 exp 14 solar mass). The very existence of such a cluster can provide interesting constraints on the relative distribution of 'visible' mass and dark matter, an important parameter in cold dark matter models for formation of structure in the universe.

Arnaud, M.↗
NASA NTRS1992

X-ray properties of bright far-infrared galaxies

The Einstein IPC was searched for observations of galaxies in the IRAS BCS. Of the 324 galaxies in this sample, 81 were observed with the IPC, and 51 were detected at a confidence level greater than 3-sigma. A strong correlation was found to exist between the FIR and X-ray luminosities among the normal and starburst (NSB) galaxies with LX varies as Lfir exp 0.90-1.01 (90-percent confidence limits). The X-ray luminosity of the 10 Seyfert galaxies in this sample is a factor of approximately 10 greater than the NSB galaxies with the same FIR luminosity. The efficiency of X-ray production through star formation is found to be nearly independent of the star formation rate with 10 exp 47.5 ergs of energy produced for each solar mass consumed into stars. It is shown that the X-ray emission from bright FIR galaxies can make a significant contribution to the observed X-ray background.

David, L. P.↗
NASA NTRS1991

Do clusters of galaxies affect the spectrum of the microwave background?

The distortion, averaged over the sky, due to the Compton scattering of background photons with electrons in the hot gas in clusters of galaxies is calculated. Using an existing sample of X-ray clusters, various values of the density parameter Omega, and plausible models for cluster evolution, Monte Carlo realizations of the microwave sky are generated. The spatial structure of these simulations shows a network of discrete sources whose properties can be a strong function of both evolution and Omega. The amount of spectral distortion in the models is greatest for models characterized by self-similar cluster evolution in an open universe and is within an order of magnitude of the current upper limits. Thus, improved observational sensitivity must inevitably detect some deviation from a blackbody spectrum.

Markevitch, M.↗
NASA NTRS1991

Ram-pressure stripping of the multiphase interstellar medium of the Virgo cluster elliptical galaxy M86 (NGC 4406)

The available infrared, optical, and X-ray data on the elliptical galaxy M86, which is experiencing strong ram-pressure stripping in the intracluster medium of the Virgo Cluster, are analyzed. A significant component of infrared 60 micron emission displaced from the center of the galaxy is found. The displaced 60 micron emission lies on the optical major axis of the galaxy in the direction of perturbations to the optical isophotes and is coincident with a small feature in X-ray emission southwest of the X-ray plume. The displaced infrared emission is interpreted in terms of collisionally heated dust exposed to hot gas where ram pressure and turbulence are disrupting the stripped interstellar medium of the galaxy. The displacement of the outer optical isophotes in the direction of the stripped gas in suggested to be due to reflection of star-light on the dust grains. Ram pressure has separated and exposed the various components of the multiphase interstellar medium of M86, enabling these constituents to be identified and analyzed separately for the first time in an elliptical galaxy.

White, David A.↗
NASA NTRS1990

The evolution of the interstellar medium in elliptical galaxies. I - The early wind phase

The evolving mass loss rates from type I and II SNe, stellar winds, and PN and the associated evolution of the mass-averaged temperature of the stellar ejecta are calculated. At early times, the mass-averaged temperature of the ejecta is found to be much greater than the central escape temperature from even very luminous elliptical galaxies due to the high frequency of type II SNe. The amount of oxygen and iron that can be injected into the intracluster medium from type II SN-driven winds in elliptical galaxies is calculated and the results are compared with observations. The gas ejected during this early wind phase is very hot and can heat the cluster gas to temperatures greater than that produced by gravitational heating alone. Two numerical simulations concerning the evolution of the ISM in an elliptical galaxy model with L(B) = 10 to the 11th solar are presented which confirm the existence of an early type II SN-driven wind phase and reproduce the observed X-ray properties of bright elliptical galaxies in the present epoch.

David, L. P.↗
NASA NTRS1990

The onset of galactic winds in early-type galaxies

Researchers report on a program using Einstein x ray observations of the x ray spectra and surface brightness profiles (or extents) of a large sample of early-type (elliptical and SO) galaxies for which the goal is to determine the critical optical luminosity for which galactic winds are important. For galaxies in which the x ray emission is dominated by hydrostatic coronae, the x ray spectra will be relatively soft (characterized by a temperature of approx. 10 to the 7th power K), while for galaxies with a galactic wind, the emission will be dominated by the spectrally harder discrete sources (since the x ray emission from the wind is essentially negligible). In this new sample of 180 galaxies, there are 28 early type galaxies with sufficient counts to obtain a spectrum with the Einstein Image Proportional Counter (IPC). This sample more than doubles the total number of early-type galaxies in earlier compilations (Forman, Jones, and Tucker 1985; Canizares et al. 1987). The new spectral observations will help determine the critical optical luminosity for the onset of galactic winds which is important for understanding the chemical evolution of galaxies and of the intergalactic medium. The implications of galactic winds for the heavy element enrichment and energy content of the intracluster medium are discussed.

Forman, W.↗
NASA NTRS1990

Gas flows in elliptical galaxies

In preparation for the next generation of x ray telescopes, researchers have begun a program investigating the evolving x ray properties of elliptical galaxies. Their galaxy models consist of a modified King profile for the luminous portion of the galaxy and can include an isothermal dark halo comprising 90 percent of the total mass. The stellar population is assumed to form at a rate which decreases exponentially on a dynamical time scale with a Salpeter initial mass function. Stellar mass loss occurs instantaneously as stars evolve off the main sequence. All stars more massive than 8 solar mass produce type II supernovae, while less massive stars loss mass through a planetary nebulae. The evolving rate of type I supernovae is normalized to a fraction, gamma sub sn I, of Tammann's (1974) value. All of this information is then incorporated into a one-dimensional hydrodynamics code to determine the evolving dynamical state of the interstellar medium.

David, L. P.↗