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At least 685 records · Page 38
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NASA NTRS1974

Midlatitude electron precipitation: A possible source of contamination of galactic X and gamma-ray measurements

The effect of trapped and precipitated particles in the magnetosphere on the measurement of galactic X-rays and gamma rays is discussed. To minimize contamination caused by electron precipitation, most galactic X-ray and gamma ray measurements are conducted at equatorial or relatively low to middle latitudes where the influence of auroral effects is expected to be small. Substorm-related VLF phase perturbations also affect the measurements. If such perturbation are indicative of electron precipitation at middle to low latitudes, then their relatively high frequency of occurrence, as many as 100 per year, is evidence that electron precipitation at these latitudes may pose a problem to some galactic X-ray and gamma ray measurements. Charts and maps are presented to show: (1) phase recordings from sixteen sub-ionospheric VLF propagation paths, (2) map of great circle propagation paths, (3) ionization rates in the nighttime ionosphere due to several sources, and (4) computer phase variation for the NLK-APL path versus electron flux for different e-folding energies.

Rosenberg, T. J.↗
NASA NTRS1974

Search for gamma ray lines from supernovae and supernova remnants

A gamma ray monitor with a NaI crystal shielded with a cup-shaped CsI cover was contained in the rotating wheel compartment of the OSO-7 spacecraft for measuring the gamma ray spectra from 0.3 to 10 MeV in search for gamma ray lines from a possible remnant in the Gum Nebula and the apparent Type I supernovae in NGC5253. A brief analysis of data yielded no positive indications for X-rays, gamma ray lines, or continuum from these sources.

Chupp, E. L.↗
NASA NTRS1974

A new measurement of the Her X-1 X-ray pulse profile

A triple peaked 1.24 sec. pulse profile in a 1-minute rocket borne exposure to Her X-1 was measured, in contrast to the doublepeaked profiles expected from models which maximize the X ray emission at the magnetic equator of an accreting neutron star. The profile exhibits statistically significant energy dependence, with the emission approximately greater than 12 keV having narrower peaks which lag (by approximately 5% of the pulse period) the corresponding peaks at lower energies. Approximately one third of the total emission from the source is nonpulsed.

Holt, S. S.↗
NASA NTRS1975

X-ray and gamma-ray astronomy

Accomplishments in the fields of X-ray and gamma ray astronomy are discussed. Data obtained from IMP and OGO satellites are analyzed to determine the sources of interplanetary radiation bursts. The energy spectrum of cosmic gamma ray bursts as observed by IMP-6 is described. The application of cooling blackbody techniques as a method for examining cosmic gamma ray bursts is reported. The experimental results and theoretical interpretation of high energy diffuse gamma rays are investigated. The structure of the SAS-2 satellite is depicted and the accomplishments are examined. Other sources of gamma radiation to include galactic fermi, Cygnus X-1, supernovae, and the planet Jupiter are proposed. Data obtained from the Pioneer 10 space probe are presented in graph form.

Source record↗
NASA NTRS1976

Production of a short-lived filament by a surge

A large surge was observed on September 17, 1971 part of which, after travelling 200,000 km across the surface, returned to the surface to form a filament. The filament lasted about 30 minutes, then rose up and returned to the source of the surge. This was interpreted as the filling of a semi-stable magnetic trap. Analysis of the microwave radio burst showed it to have been produced by a source optically thick at 8,800 MHz, with area 4 (arc min)squared and T approximately 275,000 deg, N squared sub eV approximately 7 x 10 to the 48th power. The soft x-ray burst showed a component at 12 x 1,00.000 deg with N squared sub eV approximately 3 x 10 to the 48th power.

Zirin, H.↗
NASA NTRS1976

Pulsed X-ray observations of Cen X-3 from Ariel-5

The 4.8 second X-ray pulsations from Centaurus X-3 were monitored by the MSSL collimated proportional counter on board Ariel-5 between 18-27 January 1975. Analysis of the source Doppler effect shows that the pulsation period of Cen X-3 decreased by 3.70 + or - 0.04 milliseconds during the preceding 2.3 years. The Doppler analysis also yields updated values for the binary phase and period of Cen X-3. Phase zero occurred at JD 2442438.628 + or - 0.003, and the average heliocentric binary period between October 1972 and January 1975 was 2.087129 + or - 0.000007 days. Light curves of the 4.8 second pulsations in the 3-9 keV band are characterized by two pronounced peaks, in contrast with the single peak profiles observed by Uhuru.

Tuohy, I. R.↗
NASA NTRS1976

Formation of hard X-ray tails

X-ray observations of Cygnus X-1 have shown a power-law spectrum. A natural way that this spectrum might arise is discussed. Inverse Compton scattering of a soft photon flux in a very hot accretion disk, kTe at approximately 100 keV is a possible cause. The slope of the spectrum may vary if source conditions vary.

Eardley, D. M.↗
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 NTRS1976

SAS-2 galactic gamma ray results. 2. Localized sources

Gamma-ray emission was detected from the radio pulsars PSR1818-04 and PSR1747-46, in addition to the previously reported gamma-ray emission from the Crab and Vela pulsars. Since the Crab pulsar is the only one observed in the optical and X-ray bands, these gamma-ray observations suggest a uniquely gamma-ray phenomenon occurring in a fraction of the radio pulsars. Using distance estimates it is found that PSR1818-04 has a gamma-ray luminosity comparable to that of the Crab pulsar, while the luminosities of PSR1747-46 and the Vela pulsar are approximately an order of magnitude lower. This survey of SAS-2 data for pulsar correlations has also yielded upper limits to gamma-ray luminosity for 71 other radio pulsars.

Hartman, R. C.↗
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 NTRS1976

Evidence for a 17-d periodicity from Cyg X-3

Data are presented from the Ariel-V All-Sky Monitor which indicate a 17-day periodicity of the X-ray spectra from Cyg X-3 (3U2030+40). The data are consistent with data from the Ariel V Sky Survey Experiment. Assuming that the high intensity state of Cyg X-3 is well fitted by a structureless black body (Serlemitsos et al., 1975), and that the 17-day maxima correspond to increased electron scattering in the source, it is suggested that the 17-day effect is analogous to the 35-day variation in Her X-1. The possible explanation of this phenomenon as a result of the 17-day orbital period of the binary system containing Cyg X-3 is severely constrained by the stability of the well-known 4.8-hour variation.

Holt, S. S.↗
NASA NTRS1976

The 35-d X-ray profile of Her X-1

Results of an analysis of more than 500 days of Ariel 5 All-Sky Monitor data are reported which support the view that enhanced X-ray emission from Her X-1 occurs regularly in the source's 35-day cycle. The data analyzed show that the enhancement is centered at phase 0.55 (+ or - 0.05) relative to the maximum, has an intensity of at least one-fourth of the maximum, and has an apparent duration not exceeding 10% of the 35-day cycle. It is strongly suggested that the enhancement occurs in every cycle at about one-third of the maximum.

Holt, S. S.↗
NASA NTRS1976

Vignetting characteristics of the S-056 X-ray telescope

A ray trace analysis of the vignetting characteristics of the S-056 X ray telescope is presented. The relative energy is calculated in the spot formed in the focal plane of the S-056 X ray telescope by an off axis point source at infinity for off axis angles of 0, 1, 2, ..., 35 arc minutes. At each off axis angle, the relative energies are evaluated using theoretical X ray reflectivity curves for wavelengths of 8.34 A, 17.57 A, and 27.39 A, and also using an experimental X ray reflectivity curve for 8.34 A. The effects of vignetting due purely to the geometry of the S-056 optical system are evaluated separately, as well as jointly with the effects of mirror reflectivity.

Foreman, J. W., Jr.↗
NASA NTRS1976

Recurrent X-ray outbursts from Aquila X-1

Aquila X-1 observations by the All Sky Monitor on Ariel 5 are presented. Data is compared with that obtained by rocket survey, and by the Uhuru, OSO 7, and OAO 3 satellites. The variability of brightness is discussed as a connection between dwarf novae and long term transient X ray sources.

Kaluzienski, L. J.↗
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 NTRS1977

SAS-2 galactic gamma-ray results. 2: Localized sources

Gamma ray emission was detected from the radio pulsars PSR 1818-04 and PSR 1747-46, in addition to the previously reported gamma ray emission from the Crab and Vela pulsars. Because the Crab pulsar is the only one observed in the optical and X-ray bands, these gamma ray observations suggest a uniquely gamma ray phenomenon occurring in a fraction of the radio pulsars. PSR 1818-04 has a gamma ray luminosity comparable to that of the Crab pulsar, whereas the luminosities of PSR 1747-46 and the Vela pulsar are approximately an order of magnitude lower. SAS-2 data for pulsar correlations yielded upper limits to gamma ray luminosity for 71 other radio pulsars. For five of the closest pulsars, upper limits for gamma ray luminosity are found to be at least three orders of magnitude lower than that of the Crab pulsar. Gamma ray enhancement near the Milky Way satellite galaxy and the galactic plane in the Cygnus region is also discussed.

Hartman, R. C.↗
NASA NTRS1977

X-ray topography as a process control tool in semiconductor and microcircuit manufacture

A bent wafer camera, designed to identify crystal lattice defects in semiconductor materials, was investigated. The camera makes use of conventional X-ray topographs and an innovative slightly bent wafer which allows rays from the point source to strike all portions of the wafer simultaneously. In addition to being utilized in solving production process control problems, this camera design substantially reduces the cost per topograph.

Parker, D. L.↗
NASA NTRS1977

Observations of Hercules X-1 with SAS-3 during 1975 July

X-ray pulsations from Her X-1 with energies between 0.1 and 30 keV were observed for four days with the SAS-3 satellite, during the 1975 July-August ON state of the source. The existence of a strong flux between 0.1 and 0.4 keV, with pulsations that are out of phase with those above 1 keV, is confirmed. A pulsed flux in the 19-30 keV band was discovered. The average fractional rate of change in pulse period between 1972 and 1975 was about 3 x 10 to the -6th/yr, and the absolute value of the average fractional rate of change in orbital period during the same interval was not greater than 5 x 10 to the -7th/yr

Joss, P. C.↗