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Solar X ray images obtained at solar minimum by grazing-incidence optics, noting X ray radiation spatial distribution is consistent with coronal emission models

Galactic X ray sources from Scorpio to Cygnus, establishing positions of 13 discrete sources

X ray spectra from sources in Cygnus and Scorpio, noting three strongest in Cygnus and six at low galactic longitude

Optical search of sky near X-ray positions of Cyg X-1 and Cyg X-2 for identification purposes

X-ray scanning of Cygnus region with large area proportional counters flown on attitude-controlled sounding rocket

Sounding rocket experiment to study celestial X-ray sources

Aerobee rocket experiment for detecting X-ray sources in Cygnus constellation - stellar radiation

X-ray source in Crab Nebula size and position, showing visible light distribution having common center within 15-inch precision of measurement and finite angular extent

Grazing incident double reflection X-ray telescope

Location of X-ray source Sco X-1 determined by instrumented payload flown on stabilized Aerobee rocket

Sounding rocket data analyzed for X-ray source in Scorpio constellation

Celestial observation, sounding rocket data, and emission spectrum used to identify Sco X-1 of Scorpio constellation

Optical identification of Sco X-1, Scorpio constellation

X ray astronomy observation techniques and apparatus noting detectors, data analysis problems for rocket observations and Crab Nebula, galactic and background radiation

X-ray astronomy from sounding rockets

Survey of extraterrestrial nonsolar X-radiation by Aerobee rocket measurements

Solar X-ray photographs, describing Aerobee rocket mounted telescope using grazing incidence optics

Three cosmic X-ray source locations determined, using rocket mounted Geiger counters

Spectral composition of X-ray source in Scorpius and in vicinity of Galactic centre, using rocket mounted NaI detector

Aplanatic total reflection telescope for celestial X-ray source study from rockets and satellites

Angular diameters of X-ray source regions in Scorpio and Sagittarius constellations by rocket measurement with collimator

Cosmic X-ray sources in Scorpius and Sagittarius detected by rocket flights

X ray collimating structure for focusing radiation directly onto detector

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.

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.

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.

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.

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.

The X-ray source 2U 0832-45 in the Vela X region is centered on the pulsar PSR 0833-45 and is less than 1.2 deg in extent. Weak X-ray emission is seen from two other localized regions within the radio complex, but the diffuse emission of the Vela X-ray nebula seen below 2 keV is not detected in the Uhuru energy range. We consider it likely that the X-ray source at the pulsar is being excited by the rotational energy loss of the pulsar.

The Uhuru catalog of X-ray sources is used to analyze the number versus apparent-intensity relation of X-ray objects, by constructing (log N, log S)-plots similar to those used in radio astronomy. The source number distribution is corrected for nonuniform sky coverage of the spacecraft. Two distinct distributions for objects at low (less than 20 deg) and high (more than 20 deg) galactic latitude are discussed. The distribution for low galactic latitude objects (which are mainly galactic) gives further information on their location within the Galaxy and their intrinsic luminosity. The distribution for high-latitude objects is consistent with an extragalactic origin of these sources. Evidence from the longitudinal distribution of these objects is used to further demonstrate their extragalactic nature.

Analysis of Uhuru data on the X-ray source 2U 1700-37 has revealed the presence of regular occultations. The period is 3.4 days with an occultation duration of 1.1 days. The source is highly variable on a time scale of minutes. Significant intensity variations have also been observed on a time scale of 0.1 second with a 3 sigma upper limit of 17 percent on the percentage periodically pulsed. The energy spectrum is flat and shows a large amount of low-energy absorption. The data indicate that 2U 1700-37 is an X-ray source in a binary system. The 6.6-mag O7f star HD 153919 is suggested as the optical candidate.

The X-ray source in Perseus identified as NGC 1275 is found to have a finite angular extent of about 35 arc minutes. The improved location of the center of the emission is consistent with NGC 1275. An improved location for the center of the Coma X-1 source is consistent both with the kinematic center of the cluster and with NGC 4874. These extended sources - Coma, Perseus, and the source in the Virgo cluster - may be a new class of X-ray objects associated with active galaxies in rich clusters.

A catalog of X-ray sources observed with the Uhuru satellite is presented. About 70 days of data have been analyzed for this catalog resulting in 125 sources. Approximately two-thirds of the sources are located within plus or minus 20 deg of the galactic plane. Some of the sources at higher galactic latitudes are identified with known extragalactic objects. Most of the strong sources near the galactic plane are found to be variable.

The X-ray source in the Small Magellanic Cloud SMC X-1 was observed by Uhuru on numerous occasions from December 1970 through April 1972. As previously reported by Leong et al. (1971), the source was seen to be variable. It was found that SMC X-1 occults with a period of 3.8927 days. The energy spectrum is cut off at low energies and flat. There is no large-amplitude periodic pulsation. The luminosity observed makes the binary source SMC X-1 comparable in strength to both the stronger galactic sources and the discrete sources in the Large Magellanic Cloud.

Report on the X-ray intensity observations of Cygnus X-3 performed with the aid of the X-ray satellite, Uhuru, before and during the radio flare of early September 1972. An analysis of 32 transits of the source, obtained during the period August 19 to September 6, is presented. There is no indication of an intensity change coincident with the radio flare. It is concluded that whatever precipitated the radio flare did not have a significant impact on the X-ray emitting region. Other characteristics of Cyg X-3 are also discussed.

The final report for the large orbiting X-ray telescope (LOXT) high resolution mirror design study is presented. The following tasks were performed: (1) Generation of a reference and alternate preliminary design for the LOXT high resolution mirror assembly, which will meet the LOXT scientific requirements, and are within the present state of the art of materials and fabrication techniques. (2) Measurement, in X-rays, of the scattering properties of a variety of optical flats, embodying materials, coatings, and polishing techniques which might be applicable to the flight configuration LOXT high resolution mirror. (3) Preparation of a procurement specification for a paraboloid test mirror of the size of the innermost paraboloid of the high resolution mirror assembly, including the design requirements for the reference design evolved from this preliminary design study. The results of the engineering and scientific analysis and the conclusions drawn are presented. The procurement specification for the test mirror is included.

It is shown that the X-ray source in Virgo must be intimately associated with the galaxy M87, as evidenced by the coincidence of the source centroid location with the galaxy. Although the presented results do not completely explain the origin of the X rays from the Virgo cluster, they do indicate that the bulk of the emission does not come from the nucleus or the jet, and they also indicate the presence of strong energy processes in a region surrounding M87. One view of the origin of these X rays is that they are due to relativistic electrons ejected from M87, and interacting with magnetic or radiation fields in intergalactic space by the synchrotron of inverse Compton process. The other view holds that the X rays could be due to thermal emission from a hot plasma.

We have discovered a new pulsating X-ray source with a 1.24-sec period in the constellation Hercules. Analysis of 5 months of data has shown the existence of periodic variations in the intensity of the source and correlated sinusoidal variations in the period of the 1.24-sec pulsations. As in the case of the pulsating X-ray source Cen X-3, we interpret this effect as due to an occulting binary system, with the intensity changes due to occultation of the X-ray source by its companion and with the sinusoidal variations in the period of the 1.24-sec pulsations due to the Doppler effect. In addition, we have observed a longer-time scale cycle in which the source is bright and pulsing for approximately 9 days during which we can observe the 1.7-day occulting, followed by approximately 27 days during which the source is not detected above background on individual 20-sec scans.

Evaluation of the newly published Uhuru catalog, revealing significant number of rich clusters associated with X-ray sources. Combined with earlier observations of X-ray emission from the Virgo, Coma, and Perseus clusters, this suggests that most, if not all, rich clusters include an X-ray emission region of large size and of net luminosity from 10 to the 43rd to 10 to the 44th ergs/sec.

A strong X-ray source appeared sometime between March 25 and August 17, 1971. On August 23, its intensity, as observed by the Uhuru satellite, was about twice that of the Crab Nebula, corresponding to about 3 times 10 to the -8th power ergs per sq cm per sec, in the range 2-6 keV. On December 20, 1971, its intensity had declined to one-tenth of that value in the same energy range. Its spectrum was quite steep, and fit a power law with an average energy spectral index of 3.0. The variation of X-ray intensity over a 5-month period shows qualitative differences from the previously observed transient X-ray sources, Cen XR-2 and Cen XR-4.