Quasi-sinusoidal oscillation in arrival times of pulses from NP 0532
Crab Nebula pulsar NP 0532, describing quasi- sinusoidal oscillation in arrival times of radio pulses
Counselman, C. C., III↗
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Properties of individual X-ray sources
Cosmic hard X ray sources spectra and time variations by balloons and OSO-3 satellite observations of Crab Nebula
Peterson, L. E.↗
Computer program for predicting creep behavior of bodies of revolution
Computer program, CRAB, uses finite-element method to calculate creep behavior and predict steady-state stresses in an arbitrary body of revolution subjected to a time-dependent axisymmetric load. Creep strains follow a time hardening law and a Prandtl-Reuss stress-strain relationship.
Adams, R.↗
Radio pulse shapes, flux densities, and dispersion of pulsar NP 0532
Crab Nebula pulsar NP 0532, examining radio pulse shapes, flux densities and dispersion
Campbell, D. B.↗
Physics of the neutron star
Neutron star models, discussing crystalline crust, particle superfluid properties, rotational vortices and relation to Crab Nebula pulsar
Cameron, A. G. W.↗
Acceleration and propagation of high Z cosmic rays in a pulsar environment
The survival of high Z nuclei in the X-ray photon field of a pulsar is investigated. For heavy nuclei with energies greater than or equal to 100 GeV/nucleon, 100 keV X-ray photons have sufficient energy to cause photodisintegration with cross sections of approximately 10 to the minus 25th power sq cm. Using the observed properties of the Crab pulsar, extrapolation back to epochs when the pulsar was more active indicates that the photon field is sufficiently dense to prevent the acceleration of heavy nuclei within the velocity of light cylinder. On this model, the upper limit on the energy of the escaping nuclei varies with time. The models for cosmic ray acceleration in supernova explosions or by pulsars will be related to experimental observations.
Balasubrahmanyan, V. K.↗
Ultraviolet investigations of cosmic X-ray sources and analogous objects
Data on the UV spectrum of the Crab nebula and on UV and radio frequency observations of Wolf-Rayet stars was analyzed. A description of TT Arietis is given. It is concluded that this object must be a double star, since it does not radiate like an ordinary photosphere or a single blackbody. Details of the spectrum are given.
Johnson, H. M.↗
The present state of gamma-ray astronomy.
The current state of gamma-ray astronomy is reviewed in terms of the most recent experimental results that define, in either measured fluxes or upper limits, the cosmic photon spectrum in the energy range from 0.5 MeV to 10,000 TeV. Methods of research developed during the last 10 yr are discussed and specific results are cited. Cosmic gamma rays have been observed in two regions of the spectrum - from 0.5 to 6 MeV and from about 50 MeV to several hundred mega-electronvolts. Above 50 MeV, a strong concentration of intensity is observed in a band of directions around the galactic equator. In both spectral regions a diffuse background gamma ray flux, apparently isotropic and of extragalactic origin, is observed. Evidence of 50 MeV gamma-ray pulses from the Crab pulsar has been reported. No definite evidence of any other discrete gamma-ray source besides the galaxy itself has been observed at any energy.
Clark, G.↗
Gamma-ray observations of the galactic center and some possible point sources.
A 0.5 x 0.5-m digitized spark-chamber gamma-ray telescope was flown on three balloon flights to look at the galactic center region, Virgo, and the Crab Nebula. An excess flux above atmospheric background of over 4 standard deviations was found for gamma-rays exceeding 100 MeV coming from the galactic center region, but there was no statistically significant excess in the 50-100 MeV interval. As a result, there is only a 6% chance that Compton or synchrotron radiation from electrons with a power-law spectrum having an exponent of 2.6 could make as much as a 50% contribution to the gamma-radiation in this energy range.
Fitchtel, C. E.↗
X-ray observations of pulsars.
The X-ray pulsations from NP 0532, discovered by Fritz et al. (1969), have been studied. The detectors in the investigations had wide fields of view, and the entire Crab Nebula NP 0532 radiation was detected. The power density spectrum of X-radiation observed is presented together with the shapes of X-ray and optical pulses. Searches for X-ray pulsations from other X-ray sources have also been carried out. The summarized results are shown in a table.
Bradt, H. V.↗
A new transient source observed by Uhuru.
A strong X-ray source appeared sometime between March 25 and August 17, 1971. On August 23, its intensity, as observed by the Uhuru satellite, was about twice that of the Crab Nebula, corresponding to about 3 times 10 to the -8th power ergs per sq cm per sec, in the range 2-6 keV. On December 20, 1971, its intensity had declined to one-tenth of that value in the same energy range. Its spectrum was quite steep, and fit a power law with an average energy spectral index of 3.0. The variation of X-ray intensity over a 5-month period shows qualitative differences from the previously observed transient X-ray sources, Cen XR-2 and Cen XR-4.
Matilsky, T. A.↗
Techniques in balloon X-ray astronomy.
Since the first balloon observation of the Crab Nebula balloon data have provided much information on the positions, spectra, time variability and pulsed nature of localized sources, and on the spectrum and isotropy of diffuse galactic and universal components. Measurements are limited to energies above about 20 keV by atmospheric attenuation at 2 to 3 g/sq cm depth and to below several hundred keV by detector sensitivity. Detectors usually consist of large-area Na I or Cs I scintillation counters with anticoincidence collimators for rejection of charged particles and scattered X-rays. Proportional counters are occasionally used at lower energies and solid-state detectors are used where extreme energy resolution is important. The instruments require a pointing capability on the order of 1.0 to 0.1 deg, depending on the collimator aperture. Digital data is either recorded on board or telemetered using a PCM technique.
Peterson, L. E.↗
Cooling of dense stars
Cooling rates were calculated for neutron stars of about one solar mass and 10 km radius, with magnetic fields from zero to about 10 to the 14th power gauss, for extreme cases of maximum and zero superfluidity. The results show that most pulsars are so cold that thermal ionization of surface atoms would be negligible. Nucleon superfluidity and crystallization of heavy nuclei were treated quantitatively, and more realistic hadron star models were chosen. Cooling rates were calculated for a stable hyperon star near the maximum mass limit, a medium weight neutron star, and a light neutron star with neutron-rich heavy nuclei near the minimum mass limit. Results show that cooling rates are a sensitive function of density. The Crab and Vela pulsars are considered, as well as cooling of a massive white dwarf star.
Tsuruta, S.↗
The attenuation of X-rays emitted by supernovae
The attenuation of X-rays in Arnett's C-12 detonation supernova model is computed. The attenuation of X-rays in the filaments of the Crab Nebula is computed using a model for the filaments by Woltjer and a model by Davidson and Tucker. An empirical expression by Gorenstein, Kellogg, and Gursky for the optical thickness of the interstellar medium for three supernova remnants is analyzed.
Schocken, K.↗
Stellar X-ray polarimetry on OSO-1
The importance of stellar X-ray polarimetry is reviewed. A graphite crystal polarimeter sensitive near 2.6 and 5.2 keV which was designed for the OSO-1 satellite is described. The instrument's predicted performance for many stellar X-ray sources is presented, and the fundamental questions that can be resolved with the OSO-1 polarimeter are considered. The sensitivity of the instrument is such that, during an observation time of 24 hours, the polarization of the Crab nebula can be measured with an accuracy of 0.6 percent.
Landecker, P. B.↗
Recent Observations of Cosmic Gamma Rays from 10 Mev to 1 Gev
Recent observations of cosmic gamma-rays made subsequent to the discovery of energetic photons from the galactic plane are analyzed. Three main areas under current investigation are treated. They are: (1) gamma ray emission from the plane of the galaxy, with emphasis on observations made in the vicinity of the galactic center, (2) gamma ray emission from the Crab nebula and its pulsar, and (3) diffuse gamma radiation.
Share, G. H.↗
Gamma-ray Astronomy Results Obtained in Europe Since the Iau-symposium No. 55
Results of European measurements of diffuse flux and the Crab pulsar NP 0532 are updated.
Pinkau, K.↗
The magnetospheric structure of pulsars
A model of pulsar magnetospheres is described which has evolved inductively from the work of Sturrock, where the radiation is produced near the surface of a neutron star. Some of the theoretical ideas of others, particularly those of Sturrock, are discussed. The braking index n and period-pulse-width distribution of pulsars are first reinvestigated by relaxing the conventional assumption that R sub Y = R sub L, where R sub Y is the radius of the neutral points marking the transition from closed to open magnetic field lines, and R sub L is the radius of the light cylinder. This is replaced by the parameterization R sub Y = R sub * (1- eta )power R sub L (eta), where R sub * is the neutron star radius. If the ratio frequency radiation is created near the surface and beamed along open field lines, it is found that a good fit to the period-pulse-width distribution can be obtained for eta in the range 0.5 = or eta = or 0.7. The relation n = 1 + 2 eta then gives n = 2.2 + or - 0.2, which is in good agreement with the values measured for the Crab pulsar.
Roberts, D. H.↗