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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Long-term X-ray observations of Scorpius X-1 by OSO-III.

Review of the observations of Scorpius X-1 in the energy range 7.7-22 keV provided by the X-ray telescope on the OSO-III satellite over the period from May 19 to June 13, 1967. Optical observations representative of the full range of temporal behavior of the source are available on 10 nights during this period. Sco X-1, in spite of being the most extensively observed X-ray source, remains one of the least understood. Coordinated observations in various wavelength bands, although inconclusive so far, represent potentially the most fruitful approach.

Pelling, R. M.↗
NASA NTRS1975

Results of X-ray and optical monitoring of Scorpius X-1 in 1970

Scorpius X-1 was monitored at optical and X-ray wavelengths from 1970 April 26 to 1970 May 20. 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 emission when the object was optically bright. The intensity histograms for both the optical and X-ray observations are discussed, as well as periodic variations in the optical intensity.

Mook, D. E.↗
NASA NTRS1976

The discovery of rapidly repetitive X-ray bursts from a new source in Scorpius

Rapidly repetitive X-ray bursts have been observed from a new X-ray source in Scorpius. More than 2000 bursts were observed during the 4-day continual SAS-3 observations of this source designated MXB 1730-335. The time interval between bursts varied from a minimum of about 6 s to a maximum of about 5 minutes. The energy in a given burst is approximately linearly proportional to the time interval to the next burst. The largest bursts observed last for about 60 s and represent an energy release of approximately 10 to the 40th ergs for an assumed distance to the source of 10 kpc. The smallest bursts observed last only for a few seconds. We suggest that the bursts are caused by sporadic precipitations of plasma from a reservoir in the magnetosphere of a neutron star. The reservoir is replenished at a nearly constant rate by mass transferred from a binary companion.

Lewin, W. H. G.↗
NASA NTRS1978

High energy X-ray and radio studies of Scorpius X-1

The results from extended high energy X-ray observations of Scorpius XR-1 from the OSO-8 satellite are reported here. The source was observed for a total of 15 days in 1975, 1977 and 1978. Simultaneous 10.7 GHz and 4.75 GHz radio data were obtained during the 1978 observation, and low energy X-ray data during the 1975 and 1978 observations. The data reveals a lack of any correlation between the high energy X-rays and the other energy ranges. A three standard deviation upper limit of 22% was obtained for any modulation of the high energy flux with the binary period. No high energy tail was observed at any time.

Coe, M. J.↗
NASA NTRS1979

The linear X-ray polarization of Scorpius X-1

Scorpius X-1 was observed with the Bragg crystal polarimeters aboard OSO 8 in August 1977 and again in August 1978. An analysis of these observations reveals a time-averaged polarization of 0.39% plus or minus 0.20% at 2.6 keV and 1.31% plus or minus 0.40% at 5.2 keV. The corresponding position angles are 29 deg plus or minus 10 deg and 57 deg plus or minus 6 deg, respectively. Binary phase-dependent polarization was searched for but not observed.

Long, K. S.↗
NASA NTRS1980

High energy X-ray and radio studies of Scorpius X-1

The results from extended high energy X-ray observations of Scorpius X-1 from the OSO 8 satellite are reported. The source was observed for a total of 15 days in 1975, 1977, and 1978. Simultaneous 10.7 GHz and 4.75 GHz radio data were obtained during the 1978 observation, and low energy X-ray data during the 1975 and 1978 observations. Detailed studies of the data reveal a lack of any correlation between the high energy X-rays and the other energy ranges. A 3 sigma upper limit of 22% was obtained for any modulation of the high energy flux with the binary period. No high energy tail was observed at any time.

Coe, M. J.↗
NASA NTRS1981

Soft X-ray spectral variations in Scorpius X-1

Soft X-ray spectra of Scorpius X-1 obtained with the low-energy detectors of the A-2 experiment on HEAO 1 are presented. The raw count spectra are deconvolved using the Kahn and Blissett technique to reveal the presence of oxygen absorption in the range 0.5-0.7 keV. The strength of this feature is shown to vary on a time scale of order hours. These results are interpreted as evidence for variable X-ray photoionization of circumsource material in the system. An alternative model, involving variable Compton broadening of an oxygen edge, is also discussed.

Kahn, S. M.↗
NASA NTRS1984

High-resolution soft X-ray spectra of Scorpius X-1 - The structure of circumsource accreting material

Four observations of Scorpius X-1 with the Objective Grating Spectrometer of the Einstein Observatory have provided high-resolution spectra (lambda/Delta lambda = approximately 20-50) in the wavelength range 7-46 A. The spectra reveal the presence of absorption structure due to oxygen, nitrogen, and iron, and variable emission structure associated with ionized iron and nitrogen. The strengths of these features suggest that the N/O abundance ratio in the absorbing and line emitting gas is anomalously high, which might indicate that these spectral components are associated with processed material, probably accreting matter transferred from the surface of an evolved companion. Constraints on the inclination of the system, however, imply that this cool, dense, accreting material must be well out of the plane of the binary system. Possible models for the origin and nature of this circumsource medium are discussed. An extensive discussion of the calibration of the Objective Grating Spectrometer and of the analysis of spectra acquired by that instrument is also provided.

Kahn, S. M.↗
NASA NTRS1992

X-ray variability of Scorpius X-1 during a multiwavelength campaign

Consideration is given to the X-ray variability of Scorpius X-1, which was observed with Ginga on March 9-11, 1989 as part of a multiwavelength campaign. The temporal characteristics observed, including quasi-periodic oscillations, HF noise, and VLF noise, are consistent with previous observations of Sco X-1. Quasi-periodic oscillations are observed on both the normal branch and the lower flaring branch, but not on the upper flaring branch. Limits are placed on the fractional rms variation of quasi-period oscillations on the upper flaring branch of less than or approximately equal to 2 percent of the total intensity. The characteristics of the observed red noise components are found to vary along the flaring branch. The fractional rms variation of VLF noise increases from less than 2 to greater than 6 percent as Sco X-1 moves from the flaring branch-normal branch vertex to the upper end of the flaring branch.

Hertz, P.↗
NASA NTRS1994

X-ray sources in regions of star formation. 5: The low mass stars of the Upper Scorpius association

We report followup investigations of Einstein x-ray observations of the Upper Scorpius OB association. We identify 28 low mass pre-main sequence stars as counterparts of x-ray sources in the approximately = 7 square degrees of the OB association observed. Based on kinematics and lithium abundances, these stars are low mass members of the OB association. We use optical spectra and optical and near-IR photometry to determine the stellar luminosities, effective temperatures, masses, and ages. We show that the bolometric corrections and effective temperatures of the G and K stars are consistent with those of subgiants. The low mass stars have isochronal ages of 1-2 Myr, depending on the choice of evolutionary models, with very small dispersion (sigma approximately = 1 Myr). This age is significantly younger than the 5-6 Myr found for the more massive B stars. The small dispersion in stellar ages, less than 10% the sound-crossing time of the association, suggests that star formation was triggered. We present two scenarios for star formation in this association. In the two-episode scenario, formation of the low mass stars was triggered by a supernova explosion, and the low mass stars form quickly, with high efficiency. Alternatively, high and low mass star formation was all initiated at the same time, some 5-6 Myr ago, and the apparent systematic age difference is an artifact of how the isochrones are dated. The effect of the supernova is to terminate mass accretion and yield an apparently coeval population. We show that the incompleteness in the x-ray sampling is about 65%, and is strongly dependent on stellar mass. After correction for incompleteness, we estimate there are about 2000 low mass members (stellar mass less than 2 solar mass) of this association. The mass function in this association is indistinguishable from that of the field. The ratio of naked to classical T Tauri stars is much larger than in Tau-Aur, and may be attributable to the local environment. We also present observations of eight ROX sources associated with the rho Oph cloud, and observations of non-pre-main sequence (PMS) stars in our fields.

Walter, Frederick M.↗
NASA NTRS1993

The multiplicity of T Tauri stars in the star forming regions Taurus-Auriga and Ophiuchus-Scorpius: A 2.2 micron speckle imaging survey

We present the results of a magnitude limited (K less than = 8.5 mag) speckle imaging survey of 69 T Tauri stars in the star forming regions Taurus-Auriga and Ophiuchus-Scorpius. Thirty-three companion stars were found with separations ranging from 0.07 sec to 2.5 sec, nine are new detections. This survey reveals a distinction between the classical T Tauri stars (CTTS) and the weak-lined T Tauri stars (WTTS) based on the binary star frequency as a function of separation: the WTTS binary star distribution is enhanced at the closer separations (less than 50 AU) relative to the CTTS binary star distribution. We suggest that the nearby companion stars shorten the accretion time scale in multiple star systems, thereby accounting for the presence of WTTS that are coeval with many CTTS. The binary star frequency in the projected linear separation range 16 to 252 AU for T Tauri stars (60 (+/- 17)%) is a factor of 4 greater than that of the solar-type main-sequence stars (16(+/- 3)%). Given the limited separation range of this survey, the rate at which binaries are detected suggests that most, if not all, T Tauri stars have companions. We propose that the observed overabundance of companions of T Tauri stars is an evolutionary effect, in which triple and higher order T Tauri stars are disrupted by close encounters with another star or system of stars.

Ghez, A. M.↗
NASA NTRS1998

A Multi-Year Light Curve of Scorpius X-1 Based on CGRO BATSE Spectroscopy Detector Observations

A multi-year light curve of the low mass X-ray binary, Scorpius X-1, is constructed based on the Compton Gamma-ray Observatory (CGRO) Burst and Transient Source Experiment (BATSE) Spectroscopy Detector (SD) data in the nominal energy range of 10-20 keV. A detailed discussion is given of the reduction process of the BATSE/SD data. Corrections to the SD measurements are made for off-axis pointings, spectral and bandpass changes, and differences in the eight SD sensitivities. The resulting 4.4 year Sco X-1 SD light curve is characterized in terms of the time scales over which various types of emission changes occur. This light curve is then compared with Sco X-1 light curves obtained by Axiel 5, the BATSE Large Area Detectors (LADs), and the RXTE all-sky monitor (ASM). Coincident temporal coverage by the BATSE/SD and RXTE/ASM allows a direct comparison of the behavior of Sco X-1 over a range of high energies to be made. These ASM light curves are then used to discuss model constraints on the Sco X-1 system.

McNamara, B. J.↗