Uhuru Satellite Research Articles

4U 1210−64: a new member of the rare intermediate-mass X-ray binary subclass

ABSTRACT 4U 1210−64 is a peculiar X-ray binary that was first discovered in 1978 by the Uhuru satellite. The analysis of the X-ray data revealed a 6.7-d orbital period and an additional long-term modulation that is manifested as low- and high-flux states. Based on the previous classification of the donor star from the analysis of its optical spectra, the system has been suggested to be a high-mass X-ray binary. We revisit the optical classification where, based on the spectra from the Southern African Large Telescope (SALT), we conclude that the donor star is of spectral class A8 III–IV, making it a member of the rare intermediate-mass X-ray binaries. We perform radial velocity analysis using the SALT spectra where we consider circular and eccentric orbits. From the mass function derived and the mass constraints of the donor star, we demonstrate that a neutron star is favoured as the compact object in the binary system. We show, for the first time, the folded optical light curves, whose shape is interpreted to be due to a combination of ellipsoidal variations, irradiation of the donor star, and mutual eclipses of the star and accretion disc.

Modelling of 35-d superorbital cycle of B and V light curves of IMXB HZ Her/Her X-1

ABSTRACT The X-ray binary Her X-1 consists of an accreting neutron star and the optical component HZ Her. The 35-d X-ray superorbital variability of this system is known, since its discovery in 1972 by the Uhuru satellite and is believed to be caused by forced precession of a warped accretion disc tilted to the orbital plane. We argue that the observed features of the 35-d optical variability of HZ Her can be explained by free precession of the neutron star with a period close to that of the forced disc. The model parameters include (a) the X-ray luminosity of the neutron star; (b) the optical flux from the accretion disc; and (c) the tilt of the inner and outer edges of the accretion disc. A possible synchronization mechanism based on the coupling between the neutron star free precession and the dynamical action of non-stationary gas streams is discussed.

On the nature of the 35-day cycle in the X-ray binary Her X-1/HZ Her

AbstractThe X-ray binary Her X-1 consists of an accreting neutron star and the optical companion HZ Her. The 35-day X-ray variability of this system is known since its discovery in 1972 by the UHURU satellite and is believed to be caused by forced precession of the warped accretion disk tilted to the orbital plane. We argue that the observed features of the optical variability of HZ Her can be explained by free precession of the neutron star with a period close to that of the forced disk precession. The model parameters include a) the intensity (power) of the stream of matter flowing out of the optical star; b) the X-ray luminosity of the neutron star; c) the optical flux of the accretion disk; d) the X-ray irradiation pattern on the donor star; e) the tilt of the inner and outer edge of the accretion disk. A possible synchronization mechanism based on the coupling between the neutron star free precession and the dynamical action of non-stationary gas streams is discussed shortly.

Uncovering the Nature of the X‐Ray Transient 4U 1730−22: Discovery of X‐Ray Emission from a Neutron Star in Quiescence withChandra

The X-ray transient, 4U 1730-22, has not been detected in outburst since 1972, when a single outburst was detected by the Uhuru satellite. This neutron star or black hole X-ray binary is presumably in quiescence now, and here, we report on X-ray and optical observations of the 4U 1730-22 field designed to identify the system's quiescent counterpart. Using Chandra, we have found a very likely counterpart. The candidate counterpart is close to the center of the Uhuru error region and has a thermal spectrum. The 0.3-8 keV spectrum is well-described by a neutron star atmosphere model with an effective temperature of 131+/-21 eV. For a neutron star with a 10 km radius, the implied source distance is 10(+12)(-4) kpc, and the X-ray luminosity is 1.9E33 ergs/s assuming a distance of 10 kpc. Accretion from a companion star is likely required to maintain the temperature of this neutron star, which would imply that it is an X-ray binary and therefore, almost certainly the 4U 1730-22 counterpart. We do not detect an optical source at the position of the Chandra source down to R > 22.1, and this is consistent with the system being a Low-Mass X-ray Binary at a distance greater than a few kpc. If our identification is correct, 4U 1730-22 is one of the 5 most luminous of the 20 neutron star transients that have quiescent X-ray luminosity measurements.

At the Border of Eternity

The modern epoch of great astronomical discoveries began in 1962 with x-ray observations of the sky (1), followed by observations of quasars, microwave background radiation, neutron stars as pulsars and x-ray sources, and gamma ray bursts (2). Then came hints of the most intriguing objects in the universe: black holes. To be more precise, the first indications for the existence of black holes were obtained in 1972 from the UHURU satellite x-ray observations (3) of Cyg X-1, a binary system in which the mass of the compact star exceeds the limiting mass of a stable superdense neuron star (about three solar masses). At this mass, the star should be compressed to the state of a black hole. At a recent conference (4) in Calcutta, new data from x-ray, ultraviolet, optical, and radio observations gave convincing proof of these objects, which were predicted theoretically 60 years ago (5).

Multimission observations of 4U 1538 - 52

Archival data from the eclipsing binary X-ray pulsar 4U 1538 - 52 have been analyzed. These data were obtained from four different X-ray missions and span a baseline of 12 yr. Scanning observations were made using the Uhuru satellite during May 9-15, 1972 and using HEAO A1 during August 26-31, 1977 and February 22-28, 1978. Pointed observations were made using the Einstein Observatory during March 2, 1979 and Exosat during March 17, August 7-8 and 10-11, 1984. These data are used to improve the orbital period determination, to set a limit to the change in orbital period, and to improve the knowledge of the pulse period as a function of time. Exosat pulse profiles are presented and pulse-phase spectroscopy is performed. The pulsation observations of 4U 1538 - 52 are modeled geometrically, and parameters for magnetic beaming of the accretion column are derived.

Glimpsing an Invisible Universe: The Emergence of X-ray Astronomy

Richard F Hirsh 1983 Cambridge: Cambridge University Press viii + 186 pp price £20 ISBN 0 521 25121 4 This book is a history of x-ray astronomy's infancy, from its roots in upper-atmosphere research to the UHURU satellite in the early 1970s. Hirsh analyses the roles of funding, public policy, instrumental innovation and flight opportunities, as well as the contributions of the individual scientists and their research groups.

THE HARD X-RAY FLUX FROM GAM CAS DURING 1970-73.

ABSTRACT X-ray observations are presented of the Be star Gamma Cas obtained with the Uhuru satellite between December 27, 1970, and February 15, 1973. Though variable, the X-ray source (MX 0053+60) persisted throughout the life-time of the Uhuru satellite, with an average daily flux (2-6 keV) of 4.1 counts/s or 4.0 x 10 to the 32nd ergs/s if the star is at a distance of 220 pc. Variations on time scales of months, days, and hours were observed, but a pulsation period was not found. An analysis is made of the continuous X-ray spectrum, and the X-ray flux and its behavior during the early 1970s are compared with more recent observations from the SAS-3, Copernicus, HEAO-1, and Einstein satellites.

THE VARIABLE EMISSION-LINE SPECTRUM OF HD 50896 : WN5.

ABSTRACT HD 50896 is a WN5 star whose emission-line profiles vary considerably in shape. Night-to-night changes are always present, hourly changes are usually observable, and variations are occasionally detected with a time scale of ten minutes. The radial velocity of the star has a maximum range of variation of 50 km/s. If the variability is due to binary motion, the Wolf-Rayet star has a maximum mass of 10.2 solar masses, while the companion is no larger than 1.1 solar masses. Evolutionary arguments demand that the secondary be a neutron star. The X-ray luminosity of an exposed neutron star in the Wolf-Rayet stellar wind would have been detected by the Uhuru satellite. The lack of such a detection, and the derived dimension of the orbit, imply that the neutron star, if it exists, is buried in the expanding envelope of the Wolf-Rayet primary.

Extragalactic X-ray observations - The 2A catalogue and supplementary results from the Ariel 5 sky survey

A status report is given on the Ariel 5 sky survey for X -ray sources at galactic latitude | b | ≽ 10°. The operation of the sky survey instrument (s. s. i.) is briefly reviewed and the production of the recently published 2A catalogue of X -ray sources is described. A remarkably high percentage ( ca . 75%) of the 105 sources in the 2A catalogue have now been identified with extragalactic, or, in a few cases, galactic, counterparts, and this is attributed to the improved location of sources (cf. the earlier 3U catalogue), and the strong correlation with optically bright or outstanding objects. The 2A catalogue and subsequent studies have established active galaxies, especially of the Seyfert type 1, to be a major class of powerful X -ray emitter. Present members of this class, which also includes a number of emission line galaxies, radio galaxies and quasars, are listed and their basic X -ray properties reviewed. The second major class of extragalactic X -ray source, clusters of galaxies, first established with the Uhuru satellite, has been substantially extended by Ariel 5. This work also is briefly reviewed. Finally, additional X -ray data from the s. s. i. (still operative) is being used to revise and add to the 2A catalogue. Several examples of this more recent work are given, together with an estimate of the expected content of the final s. s. i. catalogue when the mission is terminated (now planned for October 1979).

The galactic centre

While the Uhuru satellite detected an extended or multiple X-ray source located in the direction of the galactic centre, and while transient and burst sources have been found there by Ariel 5 and SAS-3, there has not so far been any detailed description of this important source. By using results from a coded mask telescope flown in 1976 on a Skylark rocket (the first successful application of such a device in astronomy) and from an extended period of observations with Ariel 5, a number of burst and ir­regular variable X-ray sources have now been discovered. In particular, the region within a few degrees of the galactic centre is evidently one of continual but irregular X-ray activity.

The detection of large X-ray halos in clusters

view Abstract Citations (35) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The detection of large X-ray halos in clusters. Forman, W. ; Jones, C. ; Murray, S. ; Giacconi, R. Abstract Evidence is presented for the existence of extended X-ray halos around several X-ray clusters. Data were analyzed from the 0.5 x 5 deg and the 5 x 5 deg collimators on the Uhuru satellite. Measured cluster intensities were compared with those detected by OSO 8 and Ariel 5 experiments. Higher counting rates for larger fields of view indicate extended X-ray emission. The implications are discussed with respect to the mass of the cluster gas and for models of supercluster X-ray emission. Publication: The Astrophysical Journal Pub Date: October 1978 DOI: 10.1086/182780 Bibcode: 1978ApJ...225L...1F Keywords: Galactic Clusters; Intergalactic Media; Satellite Observation; X Ray Astronomy; Ariel 5 Satellite; Astronomical Models; Collimators; Oso-8; Uhuru Satellite; Astronomy; Clusters of Galaxies:X Rays full text sources ADS |

The X-ray luminosity function of Abell clusters

view Abstract Citations (33) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The X-ray luminosity function of Abell clusters. Schwartz, D. A. Abstract X-ray sources identified with Abell clusters of galaxies in distance classes less than or equal to 3 give a quantitative estimate of the volume luminosity function for those clusters emitting between 10 to the 44th and 10 to the 45th power ergs/s in X-rays. At higher luminosities, tentative identifications with more distant clusters can be interpreted at least as an upper limit. This limit allows a smooth extension of the luminosity function, but with a fairly steep decrease in the range from 10 to the 45th to 10 to the 46th power ergs/s. No direct information is available for luminosities less than 10 to the 44th power ergs/s because current X-ray surveys are limited to nearby distances with very few Abell clusters; however, constraints at the low-luminosity end can be set by considering the total volume density of Abell clusters and the upper limit to the numbers of unidentified X-ray sources. The luminosity function must flatten or turn over below 10 to the 44th power ergs/s; therefore, counts of distant X-ray clusters to such a faint intrinsic luminosity can yield cosmological information. Publication: The Astrophysical Journal Pub Date: February 1978 DOI: 10.1086/155876 Bibcode: 1978ApJ...220....8S Keywords: Galactic Clusters; Stellar Luminosity; X Ray Sources; Cosmology; Globular Clusters; Spatial Distribution; Tables (Data); Uhuru Satellite; X Ray Astronomy; Astrophysics; Clusters of Galaxies:Luminosity Function; Clusters of Galaxies:X-Ray Sources full text sources ADS | data products SIMBAD (34) NED (20)

Hercules X-1 = HZ Herculis - A multiperiod variable

view Abstract Citations (19) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hercules X-1 = HZ Herculis: a multiperiod variable? Wolff, C. L. ; Kondo, Y. Abstract Fundamental rotation properties of the free modes of oscillation of a star are employed to account for the various periodicities observed in the X-ray binary system HZ Her/Her X-1. The various rotation rates may be taken as defining a set of beat periods associated with the quasiregular flareups of HZ Her. This analysis, involving only one free parameter, provides a single physical mechanism to explain five observed periods of the binary system, including periods of 1.7 days, 35 days and 10 to 12 years. Publication: The Astrophysical Journal Pub Date: January 1978 DOI: 10.1086/155821 Bibcode: 1978ApJ...219..605W Keywords: Binary Stars; Periodic Variations; Stellar Models; Variable Stars; X Ray Stars; Beat Frequencies; Mass Transfer; Stellar Rotation; Uhuru Satellite; Astrophysics; Periods:X-Ray Binaries; X-Ray Binaries: Models full text sources ADS | data products SIMBAD (1)

Long-term behavior of MXB 1730-335

view Abstract Citations (18) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Long-term behavior of MXB 1730-335. Grindlay, J. E. ; Gursky, H. Abstract The rapid burster MXB 1730-335 was detected on at least two occasions in 1971 and 1972 by Uhuru, and coverage is available from late 1970 to early 1973. Combined with ANS coverage in 1975 and 1976, as well as published SAS-3 and Ariel-5 observations (1976-1977), a unique record of long-term burst activity is now available for this source. There appear to be burst-active states of approximately one to two months' duration that occur with a duty cycle of about 15%. The burst activity appears to be recurrent with a time scale of roughly 0.5 to 1 year. Implications for burster models are discussed. Publication: The Astrophysical Journal Pub Date: December 1977 DOI: 10.1086/182588 Bibcode: 1977ApJ...218L.117G Keywords: Bursts; Periodic Variations; X Ray Sources; Ariel 5 Satellite; Astronomical Models; Spaceborne Astronomy; Stellar Mass Accretion; Uhuru Satellite; Astrophysics full text sources ADS | data products SIMBAD (7)

LMC X-1 - A luminous extended X-ray source

view Abstract Citations (7) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS LMC X-1: a luminous extended X-ray source. Epstein, A. Abstract LMC X-1 was observed by the rotating modulation collimator experiment on the SAS-3 satellite. Results of the observation include a refined position within a 30 by 40 arcsec error region. In addition, LMC X-1 is determined to have complex structure, with a 1.3-arcmin FWHM (about 10 pc) extended component accounting for most of the observed flux. The suggestion that LMC X-1 is a supernova remnant yields SNR parameters: an age of 5200 yr, a diameter of 20 pc, and an initial explosion energy of 6 by 10 to the 51st power erg. The plausibility of this model in the context of other observations is discussed. Publication: The Astrophysical Journal Pub Date: December 1977 DOI: 10.1086/182573 Bibcode: 1977ApJ...218L..49E Keywords: Galactic Structure; Supernova Remnants; X Ray Sources; Astronomical Models; Collimators; Energy Bands; Magellanic Clouds; Oao 3; Sas; Signal To Noise Ratios; Spaceborne Astronomy; Uhuru Satellite; Astrophysics full text sources ADS | data products SIMBAD (2) NED (1)

Hercules X-1 - The 1.24 second pulsation in hard X-rays

view Abstract Citations (24) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hercules X-1: the 1.24 second pulsation in hard X-rays. Kendziorra, E. ; Staubert, R. ; Pietsch, W. ; Reppin, C. ; Sacco, B. ; Truemper, J. Abstract A 4-hr balloon observation of Hercules X-1 during the ON state in the 35-day cycle was performed. The 1.24-s pulsations show a pulsed fraction of 58% + or - 8% in the 18-31-keV interval. A pulsed flux was discovered in the 31-88-keV range with a pulsed fraction of 51% + or - 14%. In the 18-60-keV range the 1.24-s pulsations are characterized by single-peaked pulses (width 250 ms FWHM), showing no significant change with energy of pulse shape and phase of the pulse maximum. At energies above 60 keV evidence is found for a double-peaked pulse profile. Publication: The Astrophysical Journal Pub Date: October 1977 DOI: 10.1086/182546 Bibcode: 1977ApJ...217L..93K Keywords: Eclipsing Binary Stars; Pulsars; X Ray Sources; Balloon-Borne Instruments; Light Curve; Oso-8; Periodic Variations; Thomson Scattering; Uhuru Satellite; Astronomy full text sources ADS |

Energy spectra of 43 galactic X-ray sources observed by UHURU

view Abstract Citations (99) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Energy spectra of 43 galactic X-ray sources observed by Uhuru. Jones, C. Abstract X-ray observations from the Uhuru satellite have been used to obtain the energy spectra from 2 to 20 keV for 43 galactic X-ray sources, which then were used to classify the X-ray sources. This survey has shown that galactic sources exhibit different spectra with a temperature range from 10 to the 7th to 2 x 10 to the 8th K. For the sources included in this survey no significant increase was observed in the number of sources with very cool temperatures or with very hot temperatures. Ten of the 11 X-ray sources which have been reported to pulsate regularly on time scales of seconds to minutes have temperatures exceeding about 10 to the 8th K. The four globular-cluster X-ray sources 3U 1820-30, 3U 1746-37, A1850 + 09, and MX 1746-20 have spectra similar to the strong galactic center sources with temperatures between 4 x 10 to the 7th and 9 x 10 to the 7th K. Publication: The Astrophysical Journal Pub Date: June 1977 DOI: 10.1086/155315 Bibcode: 1977ApJ...214..856J Keywords: Energy Spectra; Uhuru Satellite; X Ray Sources; X Ray Spectra; Binary Stars; Eclipsing Binary Stars; Galactic Radiation; Globular Clusters; Radiation Sources; Spectral Energy Distribution; Astrophysics full text sources ADS | data products SIMBAD (52)

New X-ray and radio observations of the galaxy cluster A2319

view Abstract Citations (25) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New X-ray and radio observations of the galaxy cluster A 2319. Grindlay, J. E. ; Parsignault, D. R. ; Gursky, H. ; Brinkman, A. C. ; Heise, J. ; Harris, D. E. Abstract A significantly improved position for the X-ray source 3U 1921 + 43 has been obtained by ANS and Uhuru. The combined ANS-Uhuru error box is only about 7 by 7 arcmin and is centered on the cD galaxy in the Abell 2319 cluster of galaxies. Radio observations of this cluster indicate that the emission at 610 MHz includes several discrete sources and a weak extended component. This strengthens the general association between extended radio halos and X-ray emission from clusters of galaxies. The radio halo fills the X-ray error box and is consistent with the limits reported for the angular size of the X-ray source Publication: The Astrophysical Journal Pub Date: June 1977 DOI: 10.1086/182442 Bibcode: 1977ApJ...214L..57G Keywords: Galactic Clusters; Position Errors; Radio Astronomy; X Ray Astronomy; Astronomical Netherlands Satellite; Error Analysis; Spaceborne Astronomy; Uhuru Satellite; Astronomy full text sources ADS | data products NED (2) SIMBAD (1)

X-Rays from Clusters of Galaxies

The discovery of the extended sources of X-ray emission associated with clusters of galaxies was undoubtedly one of the most significant observations carried out by the Uhuru satellite (Gursky et al (1971), Giacconi et al (1974)). At the present time, there are more than 30 identifications and suggested associations of X-ray sources with clusters of galaxies although extended emission has been directly observed in less than 10 cases.The mechanism for X-ray emission from such large objects is of considerable interest. X-rays could be generated by the inverse Compton interactions of microwave background photons with populations of relativistic electrons distributed throughout the clusters. Alternatively the radiation may be due to Bremsstrahlung from hot (T ≃ 108 °K) gas which constitutes an intracluster medium. Progress in understanding the extended X-ray sources and in determining the emission mechanism has come from observations of the X-ray structure and spectra of the cluster sources and it is the purpose of this review to present the current status of these observations.