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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
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NASA NTRS1979

The X-ray spectrum of 3C 273

An X-ray spectral measurement of the quasar 3C 273 with the HEAO-A2 experiment in June/July 1978 is reported. The best power law fit to the photon flux over the range 2-60 keV gives a slope of 1.41 + or - 0.02. However, structure is observed, indicating a slope of 1.52 between 2 keV and 9 keV and a slight flattening between 9 keV and 30 keV. Observations with the same experiment in December 1977 and OSO-8 in June 1976 allows confirmation of 40% intensity variability on the time scale of months, although within limits provided by the poorer statistical quality of the additional data no spectral change is discerned. Absorption from the source is found to be low, with the 1978 data yielding a 90% confidence upper limit to the hydrogen column density of 4.5 x 10 to the 21st power atoms/sq cm.

Worrall, D. M.↗
NASA NTRS1975

Interstellar absorption lines toward gamma Arae

The available data on interstellar absorption lines in the spectrum of gamma Ara observed from the ground and with the Copernicus telescope have been analyzed to give column densities of various ion stages of H, C, N, O, Na, Mg, Si, P, S, Ar, Ca, Mn, and Fe. The element abundances with respect to H nuclei in H I regions are similar to the values for zeta Oph, with depletions relative to the sun tending to increase with increasing condensation temperature. For example, toward gamma Ara, Fe is depleted by a factor of 50; Mg, Si, and Mn by about 10; and S, P, and N little or none. Interstellar Si IV and probably S IV appear stronger than in most other stars, but still their low ratios to Si III and S III suggest that soft X-rays and low-energy cosmic rays are not important sources of ionization. The width of the O VI lines and the absence of N V have been interpreted as evidence for a collisionally ionized region with a temperature between 300,000 and 700,000 K containing at least 0.0004 of the total interstellar column density.

Morton, D. C.↗
NASA NTRS1972

Soft X-rays from Cygnus X-2 and from Cygnus X-1 /in eclipse/.

Observations of Cygnus X-1 (probably in eclipse) and Cygnus X-2 on Oct. 23, 1971, show quite low absorption in their spectrum, and yet they are thought to be in a double or multiple star system from the optical data. The lack of intrinsic absorption in their spectra may be taken to mean that they lie sufficiently far from their primaries for a reduction to virtually zero of their interaction with the atmosphere of the primaries.

Stevens, J. C.↗
NASA NTRS1973

Spectroscopic observations of HZ Herculis. II

Preliminary results from an extensive series of spectroscopic observations of the HZ Her optical counterpart of the eclipsing, pulsating X-ray binary Her X-1. Spectrograms with a dispersion of 30 A/mm reveal a spectral type as late as F5 near minimum in the light curve with the G-band and metallic lines present. Narrow Fe lines show that HZ Her is not a rapid rotator. Low-dispersion (115 A/mm) spectra, obtained with 10-minute time resolution, reveal rapid (10-min) variations in the 4640 N III emission and in the 4471 He I absorbtion features. The H-beta absorption is variable in equivalent width, and shows evidence of being partially filled with emission.

Bopp, B. W.↗
NASA NTRS1974

International Cosmic Ray Conference, 13th, University of Denver, Denver, Colo., August 17-30, 1973, Proceedings. Volume 5

An X-ray observation of the Norma-Lupus region, charge and isotope measurements of heavy cosmic ray nuclei and their role in the determination of cosmic ray age, and the possibility of a contribution to primary cosmic ray spectra from pulsars are among the topics covered in papers concerned with some of the results of recent cosmic ray research. Other topics covered include multiple scattering of charged particles in magnetic fields, absorption of primary cosmic rays in the atmosphere, and phase lag effects on cosmic ray modulation during a recent solar cycle. Individual items are announced in this issue.

Source record↗
NASA NTRS1974

On ionization in H I regions

A comparison is made of the K I, Na I, Ca II, and H I interstellar absorption lines formed in relatively low-density interstellar clouds in H I regions. The data indicate that the fractional ionization (ratio of electron density to hydrogen density) is nearly constant for a range in hydrogen densities covering a factor of 15. If ionization balance exists in the clouds, then ionization of hydrogen by either low-energy cosmic rays or soft X-rays cannot be the principal source of the observed free electrons, and the hydrogen ionization rate is less than 10 to the -16th power per sec for these processes.

Hobbs, L. M.↗
NASA NTRS1975

ANS results on X-ray binaries

A short description is given of the Astronomical Netherlands Satellite ANS and the X-ray instruments of the Space Research Laboratory in Utrecht. ANS observed in February 1975 a soft _ KeV) X-ray flux in Her-x-I during the 'off'-state with an intensity of a factor I0 lower than observed previously in the 'on'-state. The measured uncorrected intensity is (1.1 ± 0.2)10^(-11) ergs/sq.cm sec in 0.2 - 0.28 keV at earth. The ANS observations on Cyg-X-I are summarized. Duping the May 75 flaring state a very high intensity at 0.5 keV is measured consistent with a power-law Ph0ton-spectrum with index 3.5 and an interstellar absorption of 7.10^(21) atoms/sq.cm, but not consistent with spectra that show an additional cut-off below 1KeV and an absorption of 7 10^(21) atoms/sq.cm. Intensity changes on a time scale of minutes, as observed in Cyg-X-1 lowstate, are not observed during the flaring state.

J. Heise↗
NASA NTRS1976

Stellar crystal X-ray spectroscopy on OSO-8

The large-area graphite crystal X-ray spectrometer on the OSO-8 satellite is described, and its response to stellar line and continuum radiation is discussed. A high resolution X-ray spectrum of Sco X-1 obtained from a preliminary analysis of quick look data shows a strong, smooth continuum with an absence of emission or absorption features over the energy range 2.2 to 8 keV. Upper limits are set on narrow line emission from highly ionized states of S, Ca, and Fe.

Kestenbaum, H. L.↗
NASA NTRS1976

The X-ray variability of Vela X-1 (3U 0900-40)

From observations of Vela X-1 with the MSSL 2.5-7.5 keV detector onboard Copernicus, the behavior of the source can be characterized by three phases: (1) high intensity, (2) low intensity, and (3) eclipse. Combining data from the 1972 Uhuru observations with eclipse observation yields a binary period of 8.963 + or - 0.001 days with zero phase on 1975 Feb. 6.97 + or - 0.04 UT. The low intensity phase is interpreted as being due to increased absorption in an accretion wake traveling across the line of sight (the spectral slope remains relatively constant throughout the cycle). Another period of enhanced absorption immediately after exit from eclipse may be due to a bow shock. Comparison of the two observations suggests that these structures vary from cycle to cycle and, since the orbital period is long, probably during each cycle.

Charles, P. A.↗
NASA NTRS1977

Backscatter of hard X-rays in the solar atmosphere

The solar photosphere backscatters a substantial fraction of the hard X rays from solar flares incident upon it. This reflection was studied using a Monte Carlo simulation which takes into account Compton scattering and photo-electric absorption. Both isotropic and anisotropic X ray sources are considered. The bremsstrahlung from an anisotropic distribution of electrons are evaluated. By taking the reflection into account, the inconsistency is removed between recent observational data regarding the center-to-limb variation of solar X ray emission and the predictions of models in which accelerated electrons are moving down toward the photosphere.

Bai, T.↗
NASA NTRS1976

Uhuru observations of Hercules X-1 during the low state of the 35-day cycle

X-ray emission from Her X-1 has been observed during the 23-day low state of the 35-day cycle. During this time, all the activity normally present during the high state was seen, including regular eclipses, absorption 'dips,' and 1.24-s pulsations. The present observations are compared with the models of Her X-1 derived by Roberts (1974), Gerend and Boynton (1976), Katz (1973), and Petterson (1975). It is suggested that a hot optically thin corona along both faces of the accretion disk can produce the unpulsed component of emission observed during both the high- and low-intensity states.

Jones, C.↗
NASA NTRS1978

X-ray spectra of Hercules X-1. 3: Pulse phase dependence in high energy continuum

Pulse phase-dependent spectral changes in the high energy (less than 20 keV) continuum of Hercules X-1 were observed. Cyclotron absorption of underlying continua can reproduce the observed angular dependence in the high energy cutoff. Implications of this model, which include the possibility of determining the angular separation between the line of sight and the neutron star magnetic field if the absorbing electron spectrum is known are discussed.

Pravdo, S. H.↗
NASA NTRS1978

Cyclotron lines from Her X-1

Data obtained during four balloon flight observations of hard X-ray emission from Her X-1 provide strong support for the existence of a spectral line feature at 54 keV to 58 keV, while the existence of a second harmonic is uncomfirmed. Because it is difficult to explain the observed feature by a second continuum spectrum or by atomic or nuclear processes, an interpretation in terms of a cyclotron line seems likely. There are two possibilities. There may be a cyclotron absorption feature at approximately 42 keV, and a possible second one at approximately 80 keV. In particular there may be a rather broad absorption feature between the spectral break (25 keV) and approximately 40 keV.

Truemper, J.↗
NASA NTRS1978

The case for a burst from 3U 0614+09

A single flare event with a rise time of about 7 s and a decay time of approximately 40 s was observed by the Goddard cosmic X-ray spectroscopy experiment on OSO-8 during observations of 3U 0614+09 in September 1975. The possibility is discussed that the source was 3U 0614+09, which has been compared with the low-mass binary Sco X-1. The spectra during the event could be fitted with blackbody (kT = 0.8-1.1 keV) or thermal bremsstrahlung (kT = 1.1-2.5 keV) models with absorption by cool material. In the blackbody model the source was of the order of 1 million cm in size.

Swank, J. H.↗