Dust-grain scattering of X-rays observed during the lunar occultation of a transient X-ray source near the Galactic center

1990 ◽  
Vol 353 ◽  
pp. 480 ◽  
Author(s):  
Kazuhisa Mitsuda ◽  
Toshiaki Takeshima ◽  
Tsuneo Kii ◽  
Nobuyuki Kawai
Keyword(s):  
Galactic Center ◽  
X Rays ◽  
X Ray ◽  
Lunar Occultation ◽  
Grain Scattering ◽  
Dust Grain

scholarly journals A balloon-borne X-ray survey of the central region of the galaxy

1968 ◽  
Vol 46 (10) ◽  
pp. S444-S447 ◽  
Author(s):  
Elihu Boldt ◽  
Henry Doong ◽  
Peter Serlemitsos ◽  
Guenter Riegler
Keyword(s):  
Central Region ◽  
Proportional Counter ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cesium Iodide ◽  
X Rays ◽  
Scintillation Crystal ◽  
X Ray ◽  
Gas Proportional Counter ◽  
The Galaxy

A balloon-borne X-ray survey of the galactic plane in the region of the galactic center was made from Australia during December 1966. The photon events recorded by a detector composed of a krypton gas proportional counter and a cesium iodide scintillation crystal are used to determine the spectrum of hard X-rays from the vicinity of Sgr XR-1.

scholarly journals Electron Acceleration in Short-Lived Radio Transients

1994 ◽  
Vol 142 ◽  
pp. 889-892
Author(s):  
Lewis Ball
Keyword(s):  
Galactic Center ◽  
Electron Acceleration ◽  
Radio Continuum ◽  
Initial Increase ◽  
Relativistic Electrons ◽  
X Rays ◽  
Radio Flux ◽  
Radiation Mechanisms ◽  
X Ray ◽  
Radio Transients

AbstractA short-lived (weeks-months) burst of radio emission, assumed to be synchrotron radiation, is sometimes associated with objects detected as soft X-ray transients. The “synchrotron bubble model” which has been applied to these radio transients assumes that the source is initially optically thick, and the model therefore takes no account of the details of the electron acceleration required. The initial increase in the radio flux is attributed to decreasing absorption in the expanding source. Observations of the soft X-ray transient GRS 1124 – 68 (X-ray Nova Muscae 1991) showed, for the first time, the rising phase of such a radio transient. Another radio source, the Galactic Center Transient, was discovered serendipitously in the radio and observed throughout its rise and decay. In both cases the radio flux was a decreasing function of frequency throughout the periods of increasing and decreasing flux, which is not consistent with the optically thick assumption of the synchrotron bubble model. When this assumption is discarded the mechanism responsible for producing the ultrarelativistic electrons, or at the very least the rate at which those electrons become available, must be considered. A generalization of the simple model to include a source which supplies relativistic electrons with a constant energy spectrum is discussed. While such a model can go some way toward matching the observations, it is suggested that the time is ripe for an explicit model of the electron acceleration mechanism. Some of the features such a model may have are presented.Subject headings: acceleration of particles — radio continuum: general — radiation mechanisms: nonthermal — X-rays: bursts

scholarly journals Observational results of X-Ray astronomy

1965 ◽  
Vol 23 ◽  
pp. 227-239 ◽  
Author(s):  
Par S. Bowyer ◽  
E. T. Byram ◽  
T. A. Chubb ◽  
H. Friedman
Keyword(s):  
Galactic Plane ◽  
Crab Nebula ◽  
Angular Diameter ◽  
Radio Sources ◽  
X Rays ◽  
X Ray ◽  
Lunar Occultation ◽  
Sgr A ◽  
The Crab Nebula

Ten discrete sources of X-rays have been identified from observations made with Geiger counters aboard unstabilized Aerobee rockets. The distribution of sources is flattened toward the galactic plane. Tau XR-1 is an X-ray source within one arc minute of the center of the Crab Nebula and of angular diameter one arc minute as determined from observation of a lunar occultation. The position of the strongest source, Sco XR-1, is known to about 0.5 degree and the remaining eight sources to about 1.5 degree. Three X-ray sources, Sco XR-1, Cyg XR-1, and Cyg XR-2, are not accompanied by any known optical or radio objects at their positions. Oph XR-1 matches the position of the Kepler SN 1604 and Sgr XR-1 is within 2.3 degrees of Sgr A. The remaining five sources are not sufficiently well resolved or positioned to permit identifications with optical or radio sources. The X-ray flux from the Crab Nebula is compatible with synchrotron spectrum with index — 1.1 and the flux of 1.8 × 10-8 erg cm-2 s-1 (1.5-8 Å) fits the extrapolated optical synchrotron spectrum with the same index.

scholarly journals Hard Cosmic X-Ray Sources

1973 ◽  
Vol 55 ◽  
pp. 51-73 ◽  
Author(s):  
L. E. Peterson
Keyword(s):  
Supernova Remnants ◽  
Galactic Center ◽  
Galactic Plane ◽  
Crab Nebula ◽  
X Rays ◽  
X Ray ◽  
Sky Survey ◽  
Upper Limits ◽  
Observational Status ◽  
The Crab Nebula

A review of the observational status of X-ray sources detected in the 20 ⋍ 500 keV range is presented. Of the approximately 115 sources listed in the March 1972 edition of the UHURU 2–6 keV sky survey catalog, about 15 sources have been studied in hard X-rays. Most of the data have been obtained from balloons, although the OSO-3, and more recently the OSO-7, have contributed. With the exception of CEN A, the SMC, and possibly M-87, all the sources detected at higher energies are galactic and heavily concentrated in the galactic plane. The Crab Nebula has been measured to about 500 keV in continuous emission and a component at the ⋍ 33 ms pulsar period comprising about 20% of the total emission has been detected to ∼10 MeV. Objects such as SCO-1 and CYG-2 are characterized by an exponential spectrum, which varies over a 10 min. time scale about a factor of two, and a flatter spectrum extending to above 40 keV which exhibits independent variability. Objects such as CYG-1 and possibly CYG-3 have a multi-component power law spectrum extending to over 100 keV, and may vary many factors over a period of weeks. Other sources generally not yet identified with optical or radio candidates, located in the Galactic Center and the Centaurus/Crux region also show considerable variability, and in one case may have been detected to nearly 500 keV. Only upper limits at about 2 × 10−4 photon (cm2 s keV)−1 in the 20–50 keV range exist for most supernova remnants and extragalactic sources.

scholarly journals Interstellar absorption of X-rays emitted by supernova remnants

1970 ◽  
Vol 37 ◽  
pp. 134-137
Author(s):  
P. Gorenstein ◽  
E. M. Kellogg ◽  
H. Gursky
Keyword(s):  
Supernova Remnants ◽  
Galactic Center ◽  
Crab Nebula ◽  
A Priori ◽  
Time Interval ◽  
Short Time Interval ◽  
X Rays ◽  
X Ray ◽  
The Galaxy ◽  
Cas A

An X-ray observation of the Cassiopeia Region by the ASE group from a sounding rocket on December 5, 1968, has resulted in the determination of locations for two sources that are precise to about 0.1 of a square degree. The positions of two well-known radio sources Cas A and SN 1572 (Tycho's Supernova), objects which are remnants of relatively recent galactic supernova, are consistent with these locations. Inasmuch as that region of the galaxy does not appear to contain nearly as large a concentration of objects as the galactic center, it is reasonable to make the identification between the X-ray sources and the supernova remnants on the basis of there being a small a priori probability of having an accidental coincidence within 0.1 square degrees. Cas A is almost certainly the same source as Cas XR-1 which the NRL group saw in an earlier survey [1]. During the December flight the Crab nebula was also observed for a short time interval.

White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

Chemical Species Identification in an SEM by Changes in Emitted X-Ray Energies

1974 ◽  
Vol 32 ◽  
pp. 570-571
Author(s):  
R. H. Duff
Keyword(s):  
Species Identification ◽  
Valence Electron ◽  
Chemical Species ◽  
X Rays ◽  
Chemical Bonds ◽  
Small Shift ◽  
X Ray ◽  
Electron Transitions ◽  
Peak Energy ◽  
Chemical Combination

A material irradiated with electrons emits x-rays having energies characteristic of the elements present. Chemical combination between elements results in a small shift of the peak energies of these characteristic x-rays because chemical bonds between different elements have different energies. The energy differences of the characteristic x-rays resulting from valence electron transitions can be used to identify the chemical species present and to obtain information about the chemical bond itself. Although these peak-energy shifts have been well known for a number of years, their use for chemical-species identification in small volumes of material was not realized until the development of the electron microprobe.

Influence of X-Ray Induced Fluorescence on Energy Dispersive X-Ray Analysis of Thin Foils

1977 ◽  
Vol 35 ◽  
pp. 328-329
Author(s):  
E. A. Kenik ◽  
J. Bentley
Keyword(s):  
Thin Foil ◽  
Electron Excitation ◽  
Simple Approach ◽  
Foil Thickness ◽  
X Rays ◽  
X Ray ◽  
Hole Spectrum ◽  
Illumination System ◽  
Thin Foils ◽  
Intensity Ratios

Cliff and Lorimer (1) have proposed a simple approach to thin foil x-ray analy sis based on the ratio of x-ray peak intensities. However, there are several experimental pitfalls which must be recognized in obtaining the desired x-ray intensities. Undesirable x-ray induced fluorescence of the specimen can result from various mechanisms and leads to x-ray intensities not characteristic of electron excitation and further results in incorrect intensity ratios.In measuring the x-ray intensity ratio for NiAl as a function of foil thickness, Zaluzec and Fraser (2) found the ratio was not constant for thicknesses where absorption could be neglected. They demonstrated that this effect originated from x-ray induced fluorescence by blocking the beam with lead foil. The primary x-rays arise in the illumination system and result in varying intensity ratios and a finite x-ray spectrum even when the specimen is not intercepting the electron beam, an ‘in-hole’ spectrum. We have developed a second technique for detecting x-ray induced fluorescence based on the magnitude of the ‘in-hole’ spectrum with different filament emission currents and condenser apertures.

X-ray micro tomography in the scanning electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 106-107 ◽  
Author(s):  
W. Brünger
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Target Surface ◽  
The Body ◽  
X Rays ◽  
Cross Sectional ◽  
X Ray ◽  
Micro Tomography ◽  
Scanning Electron

Reconstructive tomography is a new technique in diagnostic radiology for imaging cross-sectional planes of the human body /1/. A collimated beam of X-rays is scanned through a thin slice of the body and the transmitted intensity is recorded by a detector giving a linear shadow graph or projection (see fig. 1). Many of these projections at different angles are used to reconstruct the body-layer, usually with the aid of a computer. The picture element size of present tomographic scanners is approximately 1.1 mm2.Micro tomography can be realized using the very fine X-ray source generated by the focused electron beam of a scanning electron microscope (see fig. 2). The translation of the X-ray source is done by a line scan of the electron beam on a polished target surface /2/. Projections at different angles are produced by rotating the object.During the registration of a single scan the electron beam is deflected in one direction only, while both deflections are operating in the display tube.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

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