Observations of cosmic X-ray sources in the 10–250 keV range

1968 ◽  
Vol 46 (10) ◽  
pp. S437-S443 ◽  
Author(s):  
Laurence E. Peterson ◽  
Allan S. Jacobson ◽  
R. M. Pelling ◽  
Daniel A. Schwartz
Keyword(s):  
Power Law ◽  
Crab Nebula ◽  
Pulse Height ◽  
X Rays ◽  
Pulse Height Analyzer ◽  
X Ray ◽  
Hot Gas ◽  
Digital Format ◽  
Northern Hemispheric ◽  
The Crab Nebula

Observations of cosmic X-ray sources have been made from high-altitude balloons over Palestine, Texas, using actively collimated detectors. In this technique, a thin NaI central counter 10 to 50 cm2 in area is surrounded by a CsI well crystal shield several centimeters thick. The aperture, about 8° to 20° FWHM, is determined by either the well opening or an active honeycomb collimator. The background is determined mainly by diffuse cosmic and atmospheric X-rays entering the forward aperture. The detector is usually either servo-controlled to track the source or operated as a meridian device. Data are telemetered over the 20–250 keV range in a digital format from a 128-channel pulse-height analyzer. Several strong sources in the northern hemispheric sky have been observed. The Crab nebula has a power-law differential number spectrum with an index of –1.9 ± 0.1 and an intensity of about 10−2 photons/cm2-s-keV at 20 keV. Two observations in September 1965 and September 1966 on this object give the same flux and spectral index within about 5% over the 20–100 keV range. The source Cygnus XR-1 also has a power-law shape, very similar in slope and intensity to the Crab, which extends above background to at least 180 keV. These measurements are in general agreement with those of other workers. The power-law spectrum of the Crab and Cygnus XR-1 may be contrasted with that of SCO XR-1, which has an exponential spectrum, typical of a hot gas at 50 × 106 °K.

scholarly journals Properties of individual X-ray sources: (Invited discourse)

1970 ◽  
Vol 37 ◽  
pp. 59-80
Author(s):  
Laurence E. Peterson
Keyword(s):  
Power Law ◽  
Crab Nebula ◽  
Optical Observations ◽  
X Rays ◽  
X Ray ◽  
Upper Limits ◽  
Time Variations ◽  
Γ Rays ◽  
The Crab Nebula

Observations to determine the spectra and time variations of hard X-rays from cosmic sources have been made from balloons and from the OSO-III satellite. These data have been obtained using actively collimated scintillation counters with apertures between 6 and 24° FWHM, areas between 10 and 50 cm2 and which operate over the 10–300 keV range. The Crab Nebula has been observed on three occasions over a 22-month period between September 1965 and July 1967. The power law spectrum has a number index of 2.0 ± 0.1. No long-term changes were observed over the 30–100 keV range with a limit at 3%/yr. A balloon search with a 10 cm2 Ge(Li) detector for X-ray lines at 62.5 keV, 110 keV and 180 keV due to heavy element radioactive decays which would be produced in the initial Crab explosion based on the Cf254 hypothesis has resulted in upper limits at about 10−3 γ-rays cm2-sec. This is about a factor of 20 above the predicted levels. Simultaneous X-ray and optical observations of SCO XR-1 from OSO-III confirm that X-ray and optical flaring are indeed coincident phenomena, and that although the X-ray intensity increases about a factor of two during the flare, the equivalent temperature of the excess radiation is nearly the same as that of the quiescent object. Upper limits, 95% confidence, on the flux of M-87 at 40 keV have been obtained. These are inconsistent with the flux of 1.2 × 10−4 photons/cm2-sec-keV reported in the literature. CYG X-1 has been observed to have a power law of number index 2.0 ± 0.2. The OSO-III has observed a number of sources in the southern skies including NOR XR-2 and the variable source Centaurus XR-2.

scholarly journals The X-Ray Spectra of Cygnus XR-1 and the Crab Nebula

1968 ◽  
Vol 1 ◽  
pp. 202-205
Author(s):  
Laurence E. Peterson
Keyword(s):  
Power Law ◽  
Crab Nebula ◽  
Atmospheric Depth ◽  
Significance Level ◽  
X Ray ◽  
One Year ◽  
The Crab Nebula

In this paper we wish to present briefly the latest results which have been obtained on the hard X-ray spectra of two strong sources in the Northern skies. These observations, which have been discussed in detail previously (Peterson et al., 1967), were made from balloons launched at Palestine, Texas, to 3 gm/cm2 atmospheric depth during September 1966. The Crab Nebula and the Cygnus XR-1 were observed to have a differential number power law spectra with an index of about –2 over the 20–200 keV range. Both sources have the same intensity within about 10%. The Crab Nebula has been observed on two occasions, one year apart, and showed no change in intensity over this range at about a 5% significance level.

Escape Peaks in X-Ray Diffractometry*

1964 ◽  
Vol 8 ◽  
pp. 118-133 ◽  
Author(s):  
William Parrish
Keyword(s):  
Absorption Edge ◽  
Pulse Height ◽  
Pulse Amplitude ◽  
Silicon Powder ◽  
X Rays ◽  
Pulse Height Analyzer ◽  
Escape Peak ◽  
X Ray ◽  
Absorption Edge Energy ◽  
Detector Element

AbstractEscape peaks occur when the incident X-ray quantum, energy exceeds the absorption edge energy of the detector element and the resulting X-ray fluorescence is lost from the detector. The most common escape peaks result from 1 K-fluorescence in NaI-scintillation counters and Xe K-, Xe L-, and Kr K-fluorescence in proportional counters. The average pulse amplitude of the escape peak is proportional to the difference of the Energies of the incident and fluorescent X-rays. If the intensity of the escape peak is high as in the case of Mo Kα and a kryptoopreportional counter, and the lower level of the pulse height analyzer is raised to reject the escape peak, the quantum counting efficiency may be reduced by a factor of two. When the pulse height analyzer is set for characteristic incident radiation, escape peaks appear in powder patterns at small diffraction angles. These broad low-intensity peaks are often mistakenly identified as resulting from misalignment, scattering, etc. Each powder reflection can produce its own escape peak which occurs at an angle slightly smaller than the absorption edge of the detector element. In a silicon powder pattern the three strongest reflections produce three resolved escape peaks whose peak intensities are about 4% of their corresponding Cu Kα peaks when the X-ray tube is operated at 50 kV. The escape peak intensities decrease with decreasing X-ray tube voltage and disappear when the voltage is lower than the absorption edge energy of the detector element. Absorption edge peaks observed without the upper level of the pulse height analyzer are similar in appearance, intensity, and diffraction angle to the escape peaks. In complex powder patterns the escape peak pattern is unresolved and may produce a number of very broad peaks.

Low-energy cosmic X-ray measurements

1969 ◽  
Vol 47 (23) ◽  
pp. 2651-2666 ◽  
Author(s):  
A. J. Baxter ◽  
B. G. Wilson ◽  
D. W. Green
Keyword(s):  
Spectral Analysis ◽  
Energy Range ◽  
Crab Nebula ◽  
Spectral Characteristics ◽  
Low Energy ◽  
Data Recovery ◽  
X Rays ◽  
X Ray ◽  
Recovery System ◽  
The Crab Nebula

An experiment is described to investigate cosmic X rays in the energy range 0.25–12 keV. The data-recovery system and methods of spectral analysis are considered. Results are presented for the energy spectrum of the diffuse X-ray component and its distribution over the northern sky down to 1.6 keV with a limited extension at 0.27 keV.In the energy range 1.6 to 12 keV, the spectrum is represented by:[Formula: see text]although separate analyses indicate a flattening below 4.5 keV to give:[Formula: see text]and[Formula: see text]At the lowest energies, the flux appears to increase more rapidly and exhibits some anisotropy in arrival directions related to the gross galactic structure. Spectral characteristics of the Crab Nebula and Cygnus X-2 have also been determined.

Sky survey of high-energy cosmic X-rays and spectral information on sources in the Crab nebula, Cygnus, and Scorpius

1968 ◽  
Vol 46 (10) ◽  
pp. S409-S413 ◽  
Author(s):  
Walter H. G. Lewin ◽  
George W. Clark ◽  
William B. Smith
Keyword(s):  
Crab Nebula ◽  
High Energy ◽  
X Rays ◽  
Coma Cluster ◽  
X Ray ◽  
Sky Survey ◽  
Upper Limits ◽  
Intensity Ratios ◽  
The Crab Nebula ◽  
Made In

A complete X-ray survey of the northern sky has been made in the energy range 20–100 keV. Spectra are given for Cyg X-1 and Tau X-1. Intensity ratios (Cyg X-1/Tau X-1) of 0.84 ± 0.10 and 1.30 ± 0.25 were derived in the 20–70 keV range from data obtained on July 19, 1966 and February 13, 1967, respectively. Observations on Sco X-1 and the Coma cluster show upper limits which are quite different from results reported by other groups.

scholarly journals The electromagnetic spectrum of the Crab Nebula

1970 ◽  
Vol 37 ◽  
pp. 247-249
Author(s):  
Krishna M. V. Apparao
Keyword(s):  
Compton Scattering ◽  
Power Law ◽  
Crab Nebula ◽  
High Energy ◽  
Electromagnetic Spectrum ◽  
Microwave Region ◽  
X Ray ◽  
High Energy Electrons ◽  
Γ Ray ◽  
The Crab Nebula

The electromagnetic spectrum of the Crab Nebula has been determined experimentally in the radio, optical, and X-ray regions [1], in which it follows a power law of the type S(v) = Av−α, where S(v) is the power (in watts/m2 sec Hz), A and α are constants, and v is the frequency in Hz. Recent measurements [2–5], however, show a deviation from a power law in the microwave region (see Figure 1). In this paper, we investigate the origin of this deviation and calculate the γ-Ray spectrum due to this increase in the microwave photons via the Compton scattering from high-energy electrons.

scholarly journals Theoretical ideas concerning X-ray sources

1967 ◽  
Vol 31 ◽  
pp. 463-467 ◽  
Author(s):  
Geoffrey R. Burbidge
Keyword(s):  
Energy Source ◽  
Synchrotron Radiation ◽  
Crab Nebula ◽  
Line Spectrum ◽  
X Ray ◽  
Hot Gas ◽  
Cas A ◽  
The Crab Nebula ◽  
Thermal Bremsstrahlung

Several possible mechanisms for the emission of galactic X-ray sources are briefly reviewed. Synchrotron radiation is probably responsible for the X-ray emission from the Crab Nebula and from Cas A. The source Sco X-1 probably radiates by thermal bremsstrahlung in a cloud at 50 × 106°K, associated with an old nova. The energy source of the hot gas in such a model, and the conditions for formation of the line spectrum are considered.

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.

A Search for Soft X-Ray Sources in the Galactic Anticenter. Absorption of X-Rays from the Crab Nebula

1974 ◽  
Vol 187 ◽  
pp. 505 ◽  
Author(s):  
R. W. Hill ◽  
G. A. Burginyon ◽  
F. D. Seward ◽  
J. P. Stoering ◽  
A. Toor
Keyword(s):  
Crab Nebula ◽  
X Rays ◽  
X Ray ◽  
The Crab Nebula

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.

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