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At least 55 records · Page 3
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NASA NTRS1972

The optical polarization of Scorpius X-1.

The X-ray source Sco X-1 is known to have a slight linear polarization in visible light. An investigation was conducted to determine whether the origin of the polarization is intrinsic to the source or interstellar. No evidence could be found for unusual polarization properties in Sco X-1 that would point to an intrinsically polarized source, although this cannot be excluded. It is pointed out that the case for interstellar polarization would become very strong if stars in the immediate vicinity are found to be polarized with the same position angle.

Landstreet, J. D.↗
NASA NTRS1972

NGC 1068, 3C 273, and Scorpius X-1 - Circular polarization disputed.

Discussion of data for the Seyfert galaxy NGC 1068, the quasar 3C 273, and the X-ray source Sco X-1, for all of which it has been claimed or strongly suggested that they have large circular polarization of the order of 1% (Severny et al., 1971). In contrast the present authors obtained unambiguously null results with upper limits about 0.05% for NGC 1068 and 3C 273. For Sco X-1 no statistically significant polarization was found on three nights, and only some marginal evidence for a fluctuation or transient polarization on one night.

Kemp, J. C.↗
NASA NTRS1973

Extended X-ray and radio observations of Scorpius X-1.

A 23-day observation reveals temporal variations at energies of 3-10 keV similar to those found in previous optical data. However, there is no evidence of more than one preferred intensity level or of an intensity threshold for flares. We rule out X-ray periodicities containing more than 5 per cent of the mean quiescent-period intensity with periods of from 6 minutes to 4 hours. The X-ray intensity is strongly correlated with hardness but is not correlated with radio data collected over eight days.

Canizares, C. R.↗
NASA NTRS1974

A rapid change in the low energy cut-off of Scorpius X-1

Sco X-1 was observed on June 10, 1972 near 04 hr 33 min U.T. simultaneously in the optical (B) the soft X-ray (0.1 to 2.4 keV) and the X-ray (1.5 to 20 keV) bands of the spectrum. It is believed that a change of short duration in the absorbing medium associated with Sco X-1 was observed. The medium attenuating the low energy X-ray flux from Sco X-1 has apparently changed by more than 40% on a time scale of less than 45 sec.

Moore, W. E.↗
NASA NTRS1974

Scorpius X-1 - Origin of the radio and hard X-ray emissions

The consequences of models for the central radio source and the hard X-ray emitting region in Sco X-1 are examined. The radio emission could result from noncoherent synchrotron radiation, and the X-rays may be produced by bremsstrahlung. It is shown that both these mechanisms require a mass outflow from Sci X-1. The radio source is located at about 30 million km from the center of the star, and its linear dimensions do not exceed 300 million km. The magnetic field in the radio source is on the order of 1 gauss. If the hard X-rays are produced by thermal bremsstrahlung, their source is located between 10,000 and 50,000 km from the center of the star, the temperature is 2 billion K, and the emission measure is 2 times 10 to the 56th power per cu cm. This hot plasma loses energy inward by conduction and outward by supersonic expansion. The rates of energy loss for both of these processes are about 10 to the 36th ergs per sec, comparable to the total luminosity of Sco X-1.

Ramaty, R.↗
NASA NTRS1976

Long-term X-ray studies of Scorpius X-1. II - Evidence for flare-dominated intensity variations

Data on Sco X-1 obtained with the Ariel-5 All-Sky Monitor are analyzed for variability, and it is found that a large fraction of the X-ray emission at 3 to 6 keV can be represented by shot noise. The results indicate that almost all the emission in this range can be sensibly associated with a multiplicity of shotlike flares (about 200 a day), each having a duration of about 0.33 day. It is concluded that the overall consistency with a multiplicity of long-duration shots (rather than single flares superposed on a baseline continuum) may be generally characteristic of sources with an accretion disk.

Holt, S. S.↗
NASA NTRS1978

An upper limit to the linear X-ray polarization of Scorpius X-1

A measurement of Sco X-1 with the graphite-crystal polarimeters on the OSO 8 satellite yields upper limits (3 sigmas) to the linear polarization of 2.7% and 4.9% at 2.6 keV and 5.2 keV, respectively. The results are discussed in terms of an accretion-disk model.

Weisskopf, M. C.↗