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Internal Structures and Spectra of 3c 273 from Lunar Occultations

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THE small angular size component (3C273B) of the radio source 3C273 is generally considered to coincide with the associated quasi-stellar object (QSÖ), and the most accurate published optical and radio positions1 are consistent with this interpretation. Nevertheless, they do differ by 0.7 arc s, a discrepancy which is just outside the combined estimated errors, and the possibility of a small but significant displacement between the QSO and 3C273B cannot be excluded.
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The optical double quasar 0957+561 has been interpreted as the gravitational double image of a single object. A radio map made with the Very Large Array of the National Radio Astronomy Observatory shows unresolved sources coincident With the optical images as well as a complex of related extended emission. Although the results cannot rule out the gravitational lens hypothesis, the complex radio structure is more easily interpreted as two separate quasars. The optical and radio properties of the two quasars are so similar that the two must have been formed at the same time with similar initial conditions.
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The frequency spectrum of fluctuations caused by interplanetary scintillations may give a sensitive estimate of the diameter of a radio source. Observations of 3C 138, 3C 245, 3C 267, and 3C 273 give diameters of 0.1, ≤0.04, ≤ 0.2, and ≤ 0.02 second of arc, respectively. Resolution is at least a factor of 5 higher than that obtained to date by means of either radio interferometers or lunar occulations.
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Many difficulties face the conventional interpretation of the red shift of quasars as a Hubble shift, with associated immense distances. These objects are not of galactic size or nature, and are not associated with galaxies or clusters of galaxies. The continuing energy source for such enormous powers for a period of 10(6) to 10(7) years has not been clearly revealed. The absence of the expected absorption for the Lyman-alpha spectral line of hydrogen is a new difficulty. Because of the relativistic limit on the diameter which can produce rapid fluctuations of light output, there may not be enough surface to radiate the required light.A similar and perhaps more serious difficulty exists for the fluctuating radio output. Calculations given here for synchrotron radiation self-absorption lead to a reasonably accurate formula for the angular diameter of a radio source. For the quasar 3C 273B these relations indicate a conflict with the usually assumed distance. However, the discrepancy may be explained in terms of strong variation of radio diameter with frequency. For CTA 102 the conflict is more serious, and could be explained -for cosmological distance-only by rejecting the data of Sholomitskii. These difficulties are removed by the hypothesis that the observed quasars were ejected from a gravitational collapse at the center of our own galaxy, which may have occurred roughly 5 million years ago. The resultant distances, of the order of a million lightyears, reduce the energy problem by a factor of 10(6) or 10(7). On this basis the optical diameter would be less than a light-hour, about the size of the earth's orbit. A rotating mass of a few thousand solar masses with this diameter would account for the unusual line width, could easily produce the required radiated energy, and could readily account for observed short fluctuation periods and variations in spectrum. It is suggested that the radio output may be produced by high-speed passage of the quasar through intergalactic gas. This would probably correspond to a radio size of a few light-years or less, in agreement with the fluctuations. Since the radio power would be considerably less than that of radio galaxies, it is suggested that radio galaxies may have ejected groups of quasars. This would explain the peculiarly distant locations of the radio sources for many such galaxies. The objections to this model that have been raised are apparently not fatal. In particular, the receding hydrogen cloud discovered by Koehler to be in the line of sight to 3C 273 is more plausibly interpreted as having been ejected from our own galaxy, in the manner observed for other galaxies, than as being associated with the Virgo cluster of galaxies. The latter interpretation, which would place 3C 273 further away, is in conflict with Lyman-alpha absorption data for 3C 9 and other quasars. Thus the local model seems to give a reasonable explanation not only of quasars but also of radio galaxies, bothv of which seem largely to defy explanation on other grounds. Whether or not this model is valid, it is clear that an understanding of quasars will radically change our understanding of the universe.
Article
A mechanism is described for maser action in synchrotron sources. The process may contribute to the lowfrequency radiation from 3C273B.
Article
A RELATIONSHIP between redshift and the angular size of radio sources, particularly quasi-stellar sources, has been sought with limited success for some time. Miley1, for example, observed 72 quasi-stellar sources at 408 MHz and found that those with flat spectra and large redshift had on the average the highest fringe visibility. Bash2, however, concluded from observations of 234 radio sources at 2,695 MHz that while fringe visibility was related to spectra, no significant relation to redshift was evident.
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The first infrared (1.25 micron and 2.2 micron) observations of the jet in the quasar 3C 273 are reported. The present data, when combined with previous observations, show that the optical-infrared spectrum is a power law with index approximately equal to that in the radio, but lies a factor of 5 below the extrapolation from the radio. Various emission mechanisms for the optical-infrared jet are discussed, and it is concluded that synchrotron radiation is the most likely. However, the spectra of different parts of the jet are not the same; the radio-infrared index of the inner half is significantly larger (i.e., softer spectrum) than that of the outer half of the jet.
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Fringe amplitude measurement of 3C 273 using interferometer at 18 cm wavelength
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The radio properties ofUhuru X-ray sources with fairly certain extragalactic identifications are described briefly. Radio to X-ray flux ratios are low for rich clusters of galaxies and high for double radio sources. There is some evidence from the Abell 426 (Perseus) and Abell 1367 clusters that a radio galaxy in a rich cluster may be the centre of extended X-ray emission. Nuclei of galaxies have an enormous range in X-ray luminosity; the known range is from 1030 W for our galaxy to 31038 W for 3C 273. Unidentified X-ray sources at high galactic latitudes may include new classes of objects with very low radio to X-ray flux ratios or hard X-ray emission.
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Key Words aperture synthesis, image processing, interferometry, radio imaging, VLBI s Abstract Since the first radio astronomy observations in the 1930s, the angular resolution of radio telescopes has improved from tens of degrees to better than one thousandth of a second of arc. This advancement has been the result of technological innovations such as stable, sensitive, short-wavelength radio receivers, digital corre-lators, atomic clocks, and high-speed tape recorders, as well as the development of sophisticated image processing algorithms implemented on inexpensive, fast, digital computers.
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THE structure of 3C 273 has been studied by the technique of lunar occultation1–4, beginning with the observations by Hazard et al 1 that led to the identification of the source as a quasar. The radio source is double, with components separated by 20 arc s in position angle 43°. Component 3C 273B is compact and coincides with the optical nucleus5; component 3C 273A is extended, lying along a continuation of the optical jet. The source appears to be very narrow (
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Recent developments have greatly increased the angular resolution attainable in radio astronomy. The largest reflectors give a resolution of 2 to 3 min of are, close to that of the unaided human eye. Interplanetary scintillations and interferometry give 10^(-3) sec of arc and higher; this exceeds the resolution of Michelson's stellar interferometer by more than an order of magnitude, and is comparable to the highest resolution attained by the optical intensity interferometer (1).
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In order to investigate the physical relationship between radio and X-ray emission in quasars, the authors have observed with the Very Large Array 31 radio-loud quasars and a comparable number of radio-quiet quasars. The sample was selected to include quasars with known X-ray luminosities but poorly-known radio properties. Maps with polarization data of 15 extended radio-loud quasars at 20 cm and 6 cm are presented. They show jet magnetic fields to be aligned along the source axis while lobe fields have misaligned orientations. The authors have sought statistical associations between X-ray luminosity and extended radio luminosity, spectrum, morphology, and size in an extended sample of 44 radio-loud quasars. Only one statistically significant correlation, between X-ray and 178-MHz power, is found.
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Full-text available
The authors present B and R broadband CCD photometry of the jet of 3C 273. They find several knots within the jet. The knots at either end have a difference in color indices, with the knot at the outermost end being redder by about 1/2 magnitude in (B-R). Also, a variation in color may have been observed along the jet. This latter result would place constraints upon the jet-forming mechanism involved; the variation in color may be due to a nonthermal emission decay process. The authors discuss such mechanisms in view of these observations.
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Full-text available
Various models of the optical jet in 3C 273 are discussed. The optical emission is probably due to inverse Compton scattering of infrared radiation from the quasar by a mass in excess of about 60,000,000 solar masses. It seems that the jet was relativistically ejected along the polar axis of the quasar approximately 1 million yr ago. Difficulties are encountered in applying current models of extended radio sources to the jet.
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THE radio source 3C273 was one of the first to be identified1 with a QSO. The main features of the brightness distribution have been established from lunar occupation studies2-5, which show that the source is double, with one component coincident with a 13 mag QSO or redshift 0.158. This component, 3C273B, is variable, and has an inverted radio spectrum. The component is compact, and details of its structure have been investigated with inter-continental (VLBI) interferometers6-8. The other component, 3C273A, has a normal radio spectrum and is identified with a faint optical jet lying in position angle 223° with respect to the QSO. Component A has extended radio structure, and is not detected in VLBI observations 8. The colours of the jet indicate that the optical emission, like the radio emission from component A, is non-thermal9,10. The optical jet of 3C273 is an extremely unusual feature, and it would be interesting to make a detailed comparison of the optical and radio structure associated with the component. We provide here detailed information of the radio brightness distribution.
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An accurate radio position of the pulsar PSR 1749-28 has been derived from lunar occultations observed at Ooty. The observations have provided an independent check on the position obtained from times of arrival measurements and have considerably improved the accuracy in the position.
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