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Giacconi, R.

Publications and source records attributed to Giacconi, R..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Einstein observations of the X-ray structure of Centaurus A - Evidence for the radio-lobe energy source

The X-ray source at the center of the radio galaxy Centaurus A has been resolved into the following components with the imaging detectors on board the Einstein X-ray Observatory: (1) a point source coincident with the infrared nucleus; (2) diffuse X-ray emission coinciding with the inner radio lobes; (3) a 4-arcmin extended region of emission about the nucleus; and (4) an X-ray jet between the nucleus and the NE inner radio lobe. The 2 x 10 to the 39th ergs/s detected from the radio lobes probably arises from inverse Compton scattering of the microwave background. The average magnetic field in the SW lobe is determined to be not less than 4 microgauss. The extended region may be due to emission by a cloud of hot gas, cosmic-ray scattering, or stellar sources. The jet provides strong evidence for the continuous resupply of energy to the lobes from the nucleus.

Schreier, E. J.↗
NASA NTRS1979

X-rays from Eta Carinae and the surrounding nebula

Two X-ray pictures have been obtained of the Eta Car nebula using the imaging detectors of the Einstein Observatory. One covers a field 1-deg square with a resolution of 1 arcmin; the second covers a field 25 arcmin in diameter with resolution of a few arcsec. These show a region of diffuse X-ray emission with luminosity 10 to the 35th ergs/s. The sources have been positively identified as the peculiar object Eta Car, a Wolf-Rayet star, a cluster of O stars, and five individual O stars. The Eta Car X-ray source is extended and coincides with the outer shell of the diffuse object Eta Car itself. One X-ray bright spot may be emission from a central object within Eta Car.

Seward, F. D.↗
NASA NTRS1979

High-resolution X-ray observations of the Cassiopeia A supernova remnant with the Einstein Observatory

Cas A was observed with the imaging detectors on the Einstein X-ray Observatory. The mass of the expanding shell due to the interaction of the blast wave and the ambient medium is determined. This indicates that Cas A is probably not in the free expansion phase, but has not yet reached the adiabatic phase of expansion. Detailed comparison of X-ray, optical, and radio images shows various degrees of correlation, indicating that several processes for emission are present. An upper limit of 1,500,000 K is established for any stellar remnant that is below the expected temperature of a neutron star by a factor of about 5. The total mass of the SNR is found to be 10-30 solar masses

Murray, S. S.↗
NASA NTRS1979

A high energy astronomy overview

A technology assessment of extrasolar X-ray astronomy is presented. The role and significance of the Einstein Observatory is described.

Giacconi, R.↗
NASA NTRS1979

The Einstein /HEAO 2/ X-ray Observatory

The Einstein (HEAO 2) X-ray Observatory, launched in 1978, includes a fully imaging focusing X-ray telescope with an angular resolution of a few arc sec, a field of view of up to one deg, and a sensitivity several hundred times greater than previously available in any X-ray astronomy experiment. A high-resolution imager, an imaging proportional counter, a focal plane crystal spectrometer, and a monitor proportional counter are among the principal instruments on board the Einstein X-ray Observatory. About 20% of the total effective observing time in the first year of the X-ray astronomy experiment has been reserved for guest observers.

Giacconi, R.↗
NASA NTRS1979

Data reduction and analysis of SAS-1 data

An abstracted bibliography of 59 articles addressing the analysis of X-ray observations from the UHURU X-Ray Observatory (SAS-1) is presented. Investigations of galactic and extragalactic X-ray sources, X-ray binaries, and transient and burst phenomena are highlighted.

Giacconi, R.↗
NASA NTRS1978

Uhuru observations of X-ray emission from Seyfert galaxies

A point summation technique has been used to analyze systematically the Uhuru data for X-ray emission from the 88 Seyfert galaxies listed by Weedman (1977), plus MCG 8-11-11 reported by the Ariel 5 group. In addition to measuring the average X-ray intensity for 15 sources reported in the 4U and 2A catalogs, three new candidate sources are found. X-ray variability has previously been reported for NGC 4151, 3C 390.3, and MCG 8-11-11; Mrk 279 is now also found to vary. Furthermore, significant flaring activity from NGC 4151 was observed with as much as a factor of 10 increase in intensity on a time possibly as short as 730 seconds. The local X-ray volume emissivity of Seyfert galaxies is measured, and it is found, with standard assumptions, that from 6% to 25% of the diffuse 2-10-keV X-ray background can be attributed to emission from Seyfert galaxies. The data show that the luminosity function for X-ray Seyferts is rather steep.

Tananbaum, H.↗
NASA NTRS1978

Evidence for X-ray emission from superclusters of galaxies determined from Uhuru

X-ray emission from three class 2 clusters of rich clusters of galaxies has been detected. A definition for these objects based in part on Abell's (1961) description is used, and 12 candidate superclusters of distance class 5 and six clusters are found within the area of sky covered by the 4U catalog. The probability that these three X-ray sources accidentally coincide with the superclusters is less than 0.003. Equally low probabilities are found that the X-ray emission is due to either a single luminous cluster or to the combined emission of all members of the supercluster. A possible explanation of these sources is thermal bremsstrahlung emission from a hot tenuous gas pervading the supercluster. The mass of the gas can be as much as 10 times the mass of the galaxies in the supercluster and comparable to the virial mass necessary to bind the supercluster gravitationally. Should such regions of enhanced gas density be found to be associated with all groups of clusters (multiplicity of at least 2), this gas may provide a significant fraction of the mass required to close the universe.

Murray, S. S.↗
NASA NTRS1976

The long-term intensity behavior of Centaurus X-3

In three years of observation, the X-ray source Cen X-3 appears to alternate between 'high states', with an intensity of 150 counts/s (2-6 keV) or greater, and 'low states', where the source is barely detectable. The time scale of this behavior is of the order of months, and no apparent periodicity has been observed. Analysis of two transitions between these states is reported. During two weeks in July 1972, the source increased from about 20 counts/s to 150 counts/s. The detailed nature of this turn-on is interpreted in terms of a model in which the supergiant's stellar wind decreases in density. A second transition, a turnoff in February 1973, is similarly analyzed and found to be consistent with a simple decrease in accretion rate. The presence of absorption dips during transitions at orbital phases 0.4-0.5 as well as at phase 0.75 is discussed. The data are consistent with a stellar-wind accretion model and with different kinds of extended lows caused by increased wind density masking the X-ray emission or by decreased wind density lowering the accretion rate.

Schreier, E. J.↗
NASA NTRS1974

Uhuru observations of short-time-scale variations of the Crab

We have analyzed Uhuru X-ray observations of the Crab and found statistically significant variability in the intensity on time scales of several tenths of a second. Our results imply either that the X-ray emission from the pulsar NP 0532 is highly variable or that we have observed a previously undetected compact source of X-rays.

Forman, W.↗
NASA NTRS1974

Observations of Circinus X-1 from Uhuru

Analysis of Uhuru observations of the X-ray source Cir X-1 (3U 1516-56) suggests that the source may be a binary with a period longer than 15.0 days. Significant intensity variations have been observed on all time scales from 0.1 sec to days. Changes in the X-ray energy spectrum from 2 to 20 keV have also been found. A refined X-ray position, containing no obvious optical counterpart, is reported. The similarities between Cyg X-1 and Cir X-1 suggest that the X rays from Cir X-1 may be produced by accretion onto a massive, collapsed object.

Jones, C.↗
NASA NTRS1974

Correlation analysis of X-ray emission from Cygnus X-1

Normalized autocorrelation and cross-correlation coefficients have been calculated for the X-ray emission of Cygnus X-1 in two energy bins, 2.1-5.1 keV and 5.1-12 keV. The analysis shows a strong correlation between the pulsations in the two energy bins, with the low-energy pulsations lagging behind the high-energy ones, or alternatively a shorter duration of the pulse trains in the high-energy bin. The power spectral density derived from the autocorrelation functions indicates a larger contribution of the high-frequency components for the higher-energy X-rays.

Brinkman, A. C.↗
NASA NTRS1974

The third Uhuru catalog of X-ray sources

A new edition of the catalog of X-ray sources observed with Uhuru is presented. About 125 days of data have been analyzed for the 3U catalog, yielding a total of 161 X-ray sources. The distribution of sources is similar to that obtained for earlier editions of this catalog. Location error regions for many of the sources previously listed in the 2U catalog have been significantly reduced in size.

Giacconi, R.↗
NASA NTRS1973

On the nature of the unidentified high latitude UHURU sources

It is found that the unidentified high latitude UHURU sources can have either of two very different explanations. They must either reside at great distances with luminosity equivalent to or greater than 10 to the 46th power ergs/sec, or be contained in the galaxy with luminosity equivalent to or less than 10 to the 34th power ergs/sec. The two possibilities are indistinguishable with the available data.

Holt, S. S.↗
NASA NTRS1973

Clusters of galaxies with a wide range of X-ray luminosities.

A search through 125 days of Uhuru data for X-ray emission from X-ray sources associated with Abell clusters is reported. X rays from 16 clusters have been observed. Ten of these are newly discovered and not listed in the previous Uhuru catalog. Seven cases, where the 22 MHz flux has been measured, show a wide spread of relative X-ray and radio luminosity. The discovery of low-richness clusters with high X-ray luminosity provides a possible explanation for some of the unidentified high-latitude X-ray sources.

Kellogg, E.↗
NASA NTRS1973

X-ray observations of characteristic structures and time variations from the solar corona - Preliminary results from Skylab.

Examples taken from the S-054 X-ray telescope observations made during the first Skylab mission show the hot coronal plasma tracing the configuration of the magnetic fields. The high spectral resolution and sensitivity of the instrument has enabled the following two facts to be more firmly established: (1) that the 'quiet homogeneous corona' is in fact highly structured and that the structures observed appear to be the results of dispersed active region magnetic fields; and (2) that numerous bright points are distributed randomly on the disk. Their presence at high latitudes may play a role in solar cycle models. In addition, the capability of Skylab for studying time evolution has enabled the restructuring of coronal features to be seen at times of high activity, indicating a restructuring of the coronal magnetic fields.

Vaiana, G. S.↗
NASA NTRS1973

Further X-ray observations of Hercules X-1 from Uhuru.

Recent data are presented concerning the X-ray source Hercules X-1. Details of the 1.24-sec pulse shape and its variability are shown. The 1.24-sec period is observed to decrease with time, with an overall change of 4.5 microsec between January and July 1972. The X-ray intensity shows regular on states lasting 11 or 12 days followed by 24-day off states. While the source turn-on is not strictly periodic, the shape of the on state can be used to determine a period of 34.88 plus or minus 0.12 days for this cycle. The source turn-ons are found to only occur at one of two well-defined phases in the 1.7-day orbit.-

Giacconi, R.↗