H. Gursky

Discovery of a periodic pulsating binary X-ray source in Hercules from Uhuru.

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.

Discovery of intense X-ray bursts from the globular cluster NGC 6624

A new type of time variation of cosmic X-ray sources has been found from the Astronomical Netherlands Satellite (ANS) observations of the source 3U 1820--30 associated with the globular cluster NGC 6624. Two bursts in the approx.1--30 keV X-ray intensity of this source are reported. Each displayed a rapid rise in flux (approximately-less-than1 s) by a factor of 20--30 followed by a approx.8 s exponential decay. These bursts appear to be qualitatively different from short time variations previously reported from X-ray sources. Analysis for further source variability, energy spectra, and position is presented. The characteristics of these events may imply the existence of a collapsed core in the globular cluster. (AIP)

The UHURU catalog of X-ray souces.

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.

Discovery of the binary nature of SMC X-1 from Uhuru.

Analysis of data spanning a year of observations of the pulsating X-ray source Cen X-3 from Uhuru has revealed the existence of periodic variations in intensity of the source and correlated sinusoidal variations in the period of the 4.8-sec pulsations. We interpret this effect as due to an occulting binary system. The changes in intensity are then due to occultation of the X-ray source by a large massive companion, and the sinusoidal variations in the period of the 4.8-sec pulsations are due to Doppler effect. Physical parameters for the system are derived, and evidence for the existence and nature of an extended atmosphere surrounding the massive occulting object is discussed.

DISCOVERY OF PERIODIC X-RAY PULSATIONS IN CENTAURUS X-3 FROM UHURU.

Large amplitude periodic X ray pulsations from Centaurus X-3, observing abrupt source intensity and pulse rate changes

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-second pulse shape and its variability are shown. The 1.24- second period is observed to decrease with time, with an overall change of 4.5 mu s between 1972 January and July. The X-ray intensity shows regular on states lasting 11 or 12 days followed by 24-day off states. While ihe source turu-on is not strictly periedic, 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. In addition to the regular 1.7-day eclipses, regular dips in the X-ray intensity are seen, whose occurrence is related to the orbital phase. These dips are interpreted as absorption by gas in thc system. (auth)

AN X-RAY SURVEY OF THE CYGNUS REGION.

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

On the optical identification of Sco X-1

Optical identification of position of X-ray astronomical source Sco X-1, noting similarity of certain properties with old novae

An X-ray scan of the galactic plane from Uhuru

Galactic plane X ray scan by NASA small astronomy satellite Uhuru, discussing satellite instrumentation, detector and sensor sensitivity and preliminary measurements

X-ray pulsations from Cygnus X-1 observed from Uhuru

X ray pulsations from Cygnus X-1 observed from Uhuru satellite, suggesting exstar discovery