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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1970

Hard X-rays from Sco X-1

Hard X rays from Sco X-1, discussing high energy excess with large temporal variations

Boldt, E.↗
NASA NTRS1972

Short-term temporal studies of the X ray emission from Cas A, Tycho and Sco X-1

No evidence for stable 2-10 keV periodic emission from Cas A or Tycho in the period range 1 msec to 10 sec is found. Upper limits to the pulsed fraction are presented as a function of the assumed light curve, with absolute 99% confidence upper limits of 0.089 and 0.195 for Cas A and Tycho, respectively. Previously reported transient 1-10 Hz oscillations from Sco X-1 are not observed.

Holt, S. S.↗
NASA NTRS1972

Search for H-alpha emission from the companion radio sources of Sco X-1.

Attempt to obtain additional evidence linking three companion radio sources to Sco X-1 by the detection of optical emission from possible nebulosity in the region of the X-ray source. Further studies are required to prove that the three sources comprise a single system, since adverse weather conditions prevented needed observations during this attempt.

Vanden Bout, P. A.↗
NASA NTRS1974

Results of X-ray and optical monitoring of SCO X-1

Sco X-1 was monitored at optical and X-ray wavelengths from 1970 April 26 to 1970 May 21. The optical observations were made at six observatories around the world and the X-ray observations were made by the Vela satellites. There was a tendency for the object to show greater variability in X-ray when the object is optically bright. A discussion of the intensity histograms is presented for both the optical and X-ray observations. No evidence for optical or X-ray periodicity was detected.

Mook, D. E.↗
NASA NTRS1976

The interacting binary SCO X-1

Spectroscopic observations of Sco X-1 show conclusively that the emission lines vary in radial velocity with a period of .787 sup d + or - .006 and a full range of approximately 120 km/s. The period is identical to that found by Gottleib et al (1975) from photometric data; light minimum occurs when the emission line region is at superior conjunction. The observations indicate that the emission lines originate in an accretion disk surrounding a neutron star which is orbiting about a normal, although somewhat evolved companion. The light variation is due to a heating effect on the non degenerate star, viewed at a small inclination angle.

Cowley, A. P.↗
NASA NTRS1980

A high sensitivity determination of the hard X-ray spectrum of Sco X-1

The results of hard X-ray observations of Sco X-1 by HEAO 1 and OSO 7 are reported. The X-ray spectrum between 20 and 70 keV was found consistent with thermal bremsstrahlung from a hot plasma at a temperature of 5.15 plus or minus 0.05 keV. Observations with the instruments of HEAO 1 on Sept. 6-7, 1978, and with those of OSO 7 during 1972, have not confirmed reports that the bremsstrahlung spectrum is accompanied by an extra component at energies greater than 40 keV - the reported observations yield a two-standard deviation upper limit to the flux in this region of 6.4 x 10 to the -6th photons/sq cm/s/keV.

Rothschild, R. E.↗
NASA NTRS1980

The discovery of 'Sco X-1 type' behaviour from the X-ray burster 4U 1735 - 44

A series of Copernicus, Ariel V and optical observations of the X-ray burst source 4U 1735 - 44 (= MXB 1735 - 44) revealed properties very similar to those of the 'Sco X-1 like' sources. During one run, the non-burst X-ray flux varied by a factor of 2 on a time-scale of hours and this was associated with a general hardening of the spectrum. The source was relatively constant throughout the remaining observations. An Ariel V spectrum obtained during a quiescent interval deviated from a simple thermal model in that it showed both a high energy deficiency and a low energy excess. Near simultaneous spectroscopy of the optical counterpart confirmed the general features reported by McClintock et al. Spectra taken on successive nights revealed the H-beta emission to be variable.

White, N. E.↗
NASA NTRS1985

Bimodal quasi-oscillatory and spectral behavior in Sco X-1

X-ray observations were made to follow up the discovery of quasi-periodic oscillations (QPO) in Sco X-1. The QPO is observed in the quiescent state, and between flares in the active state. When the source is quiescent, the QPO frequency is 6 Hz and anticorrelated with intensity; in the active state, the frequency ranges from 10 to 20 Hz and is strongly correlated with intensity. At high intensities the QPO dissolves into continuum noise. The QPO rms amplitude decreases with count rate, and increases with photon energy. There are two modes of spectral behavior, with a one-to-one correspondence to the two modes of QPO: the spectral hardness ratio varies more steeply with intensity when the source shows 6 Hz QPO, than for 10 to 20 Hz QPO. Transitions between QPO modes, which occur when the flux is at its lowest levels, correspond to transitions between hardness ratio modes. The QPO frequency changes continuously through the transitions, which last a few hundred seconds.

Priedhorsky, W.↗
NASA NTRS1998

Very Rapid Phenomena in Sco X-1

With the launch of the Rossi X-ray Timing Explorer the high-frequency part of the power density spectra became for the first time accessible to astronomers. The main result of the project supported by grant NAG5-3271 is our discovery of quasi-periodic oscillations (QPOs) in the kiloHertz range for Sco X-1. This discovery has been followed by detections of kHz QPOs in numerous other X-ray binary sources. This has been one of the most fruitful areas of research for the Rossi XTE. The physical interpretation of these QPOs is, as yet, unclear.

VanParadijs, Johannes A.↗
NASA NTRS2001

Thermodynamic Database for the NdO(1.5)-YO(1.5)-YbO(1.5)-ScO(1.5)-ZrO2 System

A database for YO(1.5)-NdO(1.5)-YbO(1.5)-ScO(1.5)-ZrO2 for ThermoCalc (ThermoCalc AB, Stockholm, Sweden) has been developed. The basis of this work is the YO(1.5)-ZrO2 assessment by Y. Du, Z. Jin, and P. Huang, 'Thermodynamic Assessment of the ZrO2-YO(1.5) System'. Experimentally only the YO(1.5)-ZrO2 system has been well-studied. All other systems are only approximately known. The major simplification in this work is the treatment of each single cation unit as a component. The pure liquid oxides are taken as reference states and two term lattice stability descriptions are used for each of the components. The limited experimental phase diagrams are reproduced.

Jacobson, Nathan S.↗
NASA NTRS2011

Modeling the Oxygen K Absorption in the Interstellar Medium: An XMM-Newton View of Sco X-1

We investigate the absorption structure of the oxygen in the interstellar medium by analyzing XMM-Newton observations of the low mass X-ray binary Sco X-1. We use simple models based on the O I atomic cross section from different sources to fit the data and evaluate the impact of the atomic data in the interpretation of astrophysical observations. We show that relatively small differences in the atomic calculations can yield spurious results. We also show that the most complete and accurate set of atomic cross sections successfully reproduce the observed data in the 21 - 24.5 Angstrom wavelength region of the spectrum. Our fits indicate that the absorption is mainly due to neutral gas with an ionization parameter of Epsilon = 10(exp -4) erg/sq cm, and an oxygen column density of N(sub O) approx. = 8-10 x 10(exp 17)/sq cm. Our models are able to reproduce both the K edge and the K(alpha) absorption line from O I, which are the two main features in this region. We find no conclusive evidence for absorption by other than atomic oxygen.

Garcia, J.↗