Showing papers on "Radio wave published in 1968"
TL;DR: In this article, the first report of a curious class of astronomical radio sources, distinguished by their rapid and extremely regular pulsations, was made by Hewish et al. They are now understood to be rapidly rotating, magnetized neutron stars, or pulsars.
Abstract: Unusual signals from pulsating radio sources have been recorded at the Mullard Radio Astronomy Observatory The radiation seems to come from local objects within the galaxy, and may be associated with oscillations of white dwarf or neutron stars 1968 saw the first report of a curious class of astronomical radio sources, distinguished by their rapid and extremely regular pulsations Hewish et al associated them with unusually stable oscillations in compact stars They are now understood to be rapidly rotating, magnetized neutron stars, or pulsars
1,554 citations
1,440 citations
TL;DR: The constancy of frequency in the recently discovered pulsed radio sources can be accounted for by the rotation of a neutron star as discussed by the authors, where relativistic velocities will set up in any plasma in the surrounding magnetosphere, leading to radiation in the pattern of a rotating beacon.
Abstract: The constancy of frequency in the recently discovered pulsed radio sources can be accounted for by the rotation of a neutron star. Because of the strong magnetic fields and high rotation speeds, relativistic velocities will be set up in any plasma in the surrounding magnetosphere, leading to radiation in the pattern of a rotating beacon.
651 citations
TL;DR: In this paper, the long period fluctuations in the amplitudes of radio signals from the pulsed sources from the interstellar medium have been investigated, and it was shown that these fluctuations may be caused by irregularities in the medium.
Abstract: Refraction by irregularities in the interstellar medium may cause the long period fluctuations in the amplitudes of radio signals from the pulsed sources.
178 citations
132 citations
TL;DR: In this article, a two-scale model of rough surfaces is considered which permits theoretical interpretation of the features of very high frequency (VHF) scattering from such surfaces (say, from a sea surface).
Abstract: A two-scale model of rough surfaces is considered which permits theoretical interpretation of the features of very high frequency (VHF) scattering from such surfaces (say, from a sea surface). The scattering surface is assumed to be a superposition of small-scale ripple and large waves (swell). Reflection from the latter may he considered by the Kirchhoff approximation. The spatial spectrum of corrugations is taken into consideration; the calculations based on this model help to give an explanation of the behavior of the scattered intensity as a function of the angle of incidence \psi , and to establish which factors affect this dependence at various values of \psi - Theoretically predicted dependence of the scattered intensity upon radio wavelength \lambda , depolarization of the scattered signal, and other features of the scattered radiation are in good agreement with the experimental data obtained from direct measurements. Frequency spectra of the backscattered signal were also investigated (experimental measurements were carried out at wavelengths 3.2 cm, 10 cm, 50 cm, 1.5 m, and 4 m). Observed shifts of the central frequency agree with results of other authors (for the range of \lambda = 3 cm to 200 m). The measured values of the spectrum width appeared approximately twice those theoretically calculated. This may be explained by the influence of dissipative processes and of fluctuations of the skin-deep layer drift velocities. Space correlation of the backscattered signal was also investigated (both theoretically and experimentally). 50 percent decorrelation occurs at distances compared with dimensions of a wave slope.
117 citations
TL;DR: In this article, the authors correlated solar flare X ray bursts detected by OGO spacecraft correlated with radio emission and solar flare electron and proton events, and showed that radio emission is correlated with solar flare electrons and positron events.
Abstract: Solar flare X ray bursts detected by OGO spacecraft correlated with radio emission and solar flare electron and proton events
97 citations
87 citations
85 citations
TL;DR: In this article, the details of three of the four pulsating radio sources discovered at Cambridge have been given, and the four sources are described in detail. But no details of the other two sources are given.
Abstract: Details are now given of three of the four pulsating radio sources discovered at Cambridge.
83 citations
TL;DR: Radio spectral line emission from hydroxyl radicals has been detected from four infrared stars and the emission from the infrared star NML Cygni at 1612 megahertz is the strongest radio emission line yet detected.
Abstract: Radio spectral line emission from hydroxyl radicals has been detected from four infrared stars The emission from the infrared star NML Cygni at 1612 megahertz is the strongest radio emission line yet detected Sixteen other stars with infrared excesses showed no detectable hydroxyl radio emission
TL;DR: In this article, the authors reported the successful detection of linear polarization in all of the four known sources, including the pulsating stars, in the wide frequency band over which intense radiation is emitted simultaneously.
Abstract: The mechanism of emission from the pulsating radio sources reported by Hewish et al.1 seems to be quite different from that of any other celestial radio source, particularly because of the wide frequency band over which intense radiation is emitted simultaneously2. An analogy may be found, however, in the radio pulse emitted by a cosmic ray shower3,4, in which a sheet of particles moving relativistically may emit linearly polarized radiation when they are deflected by the Earth’s magnetic field. It seemed appropriate therefore to search for linear polarization in the pulsating stars, and we here report the successful detection of linear polarization in all of the four known sources.
TL;DR: In this paper, the three other sources reported by Hewish et al. 1 have been studied with the 250 ft. telescope at Jodrell Bank at frequencies of 151 MHz, 408 MHz and 922 or 1,412 MHz, to obtain the spectrum of the radio emission and compare the shapes of the pulses emitted by the four known sources.
Abstract: Following the observations1,2 of the pulsating radio source CP 1919 at α = 19h19m, δ = 21° 47′, the three other sources reported by Hewish et al. 1 have been studied with the 250 ft. telescope at Jodrell Bank. Simultaneous observations have been made on frequencies of 151 MHz, 408 MHz and 922 or 1,412 MHz, to obtain the spectrum of the radio emission and to compare the shapes of the pulses emitted by the four known sources.
TL;DR: In this article, a simplified approximate equation has been developed to predict the frequencies at which these electrostatic resonances should appear in a plasma irradiated with radio waves at frequencies for which the group velocity of the electrostatic waves is zero or small.
Abstract: THE theory of electrostatic waves is highly developed1–3. The propagation of electrostatic waves has been observed in laboratory plasmas by measuring the time required for a pulse of these waves to travel between antennae imbedded in the plasma4. Resonance phenomena have been expected to appear in a plasma irradiated with radio waves at frequencies for which the group velocity of the electrostatic waves is zero or small. This concept has been used5 to explain certain previously observed resonances. Bernstein's theory, however, also predicts zero group velocity at frequencies for which resonances have not previously been observed. A simplified approximate equation has been developed by Stix6 and improved by Dougherty and Monaghan7 to predict the frequencies at which these electrostatic resonances should appear. The resonances observed by instruments carried on satellites may correspond to a finite group velocity that matches the velocity of the satellites.
TL;DR: In this article, preliminary results of observations made at the Arecibo Ionospheric Observatory with equipment adjusted to give a time resolution of 0·1 ms were presented. But these results were only applied to pulses with a single energy from CP 0950 and CP 1133.
Abstract: Pulsars have so far been observed with time constants and radio frequency bandwidths giving time resolutions of about 1 ms or more1–4. We present here preliminary results of observations made at the Arecibo Ionospheric Observatory with equipment adjusted to give a time resolution of 0·1 ms. With this arrangement, pulse structure possessing circular polarization with time scales of the order of 0·2 ms has been seen within single energy from CP 0950 and CP 1133 (reported at the Conference on Rapidly Pulsating Radio Sources, May 1968). Similar short time structure for CP 0950 at a frequency of 2,295 MHz was also reported at the conference by R. D. Ekers and A. T. Moffet. J. H. Taylor has reported observations of occasional circularly polarized pulses made on a lower frequency and with a longer time constant.
TL;DR: In this paper, an approximate theory of multimode propagation in a nonuniform curved terrestrial waveguide is presented, where the starting point is the calculation of the mode conversion in a waveguide with an abrupt change of reflecting height and wall impedance.
Abstract: An approximate theory of multimode propagation in a nonuniform curved terrestrial waveguide is presented. The starting point is the calculation of the mode conversion in a waveguide with an abrupt change of reflecting height and wall impedance. The extension to cascaded sections is then developed. Other approaches are also considered. Finally, some attention is paid to the influence of the angle between the direction of propagation and the terminator (i.e., the sunrise or sunset line). Although no detailed comparison between theory and experiment is made, the results are compatible with much of the observational data reported in the literature.
TL;DR: In this paper, an interferometric study of an OH emission source in W3 /IC 1795/ region, processing data on digital computer is presented, where the authors use a digital computer.
Abstract: Interferometric study of OH emission source in W3 /IC 1795/ region, processing data on digital computer
TL;DR: In this article, it was decided to search for radio pulses from this source at these receiver frequencies, which were above that of the original observation at 81 MHz, the first observation being on February 24, 1968.
Abstract: At the time of publication of the remarkable discovery by a group of Cambridge radio astronomers1 of the pulsating radio source at α = 19h19m39s ± 3s, δ= +22° ± 30′ (1950), the mark I radio telescope was equipped for reception at frequencies of 151, 240 and 408 MHz. The receivers were intended for studies of flare stars and interplanetary scintillations, and an Argus 400 digital computer was in use for the on-line analysis of the receiver outputs. It was therefore decided to search for radio pulses from this source at these receiver frequencies, which were above that of the original observation at 81 MHz. Radio pulses were found at all three frequencies, the first observation being on February 24, 1968. The position of the source agreed well with the original observations; the declination was measured as 21° 40′ ± 7′ (1950).
TL;DR: In this article, measurements of the spectrum of the pulsed radio sources, the characteristics of the intensity variations at different frequencies, and observations of the structure and polarization of the pulses are presented.
Abstract: The pulsed radio sources1,2 emit energy almost simultaneously over a wide frequency band3. Pulses from the source at 19h 19m 37s, + 21°47′02″ (epoch 1950) have been received with the Australian 210 ft telescope at frequencies of 85, 150, 630, 1,410 and 2,700 MHz. This report covers measurements of the spectrum of the pulses, the characteristics of the intensity variations at different frequencies, and observations of the structure and polarization of the pulses. A previous communication4 discussed measurements of the period of the pulses and of the dispersion between 85 and 1,410 MHz.
TL;DR: In this paper, the authors measured the flux density of Sco X-1 at a wavelength of 4.6 cm, which is substantially below the previously determined upper limits of 0.021 ± 0.007 flux units.
Abstract: SOME twenty X-ray sources are now known, among them the well known objects M87 and the Crab nebula. Two X-ray sources (Sco X-1 and Cyg X-2) have been optically identified with previously unknown objects which have a stellar appearance and the characteristics of old novae1,2. Most X-ray sources remain unidentified, however. Most of them lie at low galactic latitudes, and it seems possible that many are objects similar to Sco X-1. These objects are not prominent at radio wavelengths and previous attempts to detect radio emission from Sco X-1, the strongest X-ray source, have yielded only upper limits to its flux density (refs. 3–5 and Hogg and Johnson quoted in ref. 6). The flux density of Sco X-1 has now been measured as 0.021 ± 0.007 flux units (1 flux unit = 10−26 W m−2 Hz−1) at a wavelength of 4.6 cm. This value is substantially below the previously determined upper limits.
TL;DR: The linear polarization of the radio emission from the pulsating radio stars provides an opportunity for the first direct measurement of the average magnetic field over distances of up to 100 pc from the Sun.
Abstract: The discovery of linear polarization of the radio emission from the pulsating radio stars1 provides an opportunity for the first direct measurement of the average magnetic field over distances of up to 100 pc from the Sun. It has already been shown2,3 that the frequency dispersion in arrival time of the pulses can be entirely explained by a dispersion in group velocity in ionized interstellar gas, and for the pulsating star CP 1919 the integrated electron density ∫N dl along the line of sight has been found3 to be 12·55 cm-3 pc. If a magnetic field has a component H 11 along the line of sight, then the Faraday rotation of the plane of polarization is a measure of ∫N H 11 dl; the ratio of the two integrals then gives H 11, the average value of H 11 along the line of sight, weighted according to the electron density.