Intense Radio Sources Research Articles

Infrared Emission from the Radio Supernebula in NGC 5253: A Proto–Globular Cluster?

Hidden from optical view in the starburst region of the dwarf galaxy NGC 5253 lies an intense radio source with an unusual spectrum, which could be interpreted variously as nebular gas ionized by a young stellar cluster or nonthermal emission from a radio supernova or an active galactic nucleus. We have obtained 11.7 and 18.7 μm images of this region at the Keck telescope and find that it is an extremely strong mid-infrared emitter. The infrared-to-radio flux ratio rules out a supernova and is consistent with an H II region excited by a dense cluster of young stars. This supernebula provides at least 15% of the total bolometric luminosity of the galaxy. Its excitation requires 105-106 stars, giving it the total mass and size (1-2 pc diameter) of a globular cluster. However, its high obscuration, small size, and high gas density all argue that it is very young, no more than a few hundred thousand years old. This may be the youngest globular cluster yet observed.

Radio Patrol Camera for Supernovae Search

Zwicky started extragalactic supernovae patrol using 10 inch Schmidt camera about fifty years ago. After that the research of supernovae was accelerated, because the wide view of the Schmidt camera made it possible to watch large field of the sky. The key technology of the Schmidt camera was its sophisticated optical system.Anticipated next supernova in our Galaxy may be undetectable by the optical instrument due to the Galactic extinction. However, supernovae are now known to be intense radio sources after a year or so of the explosion. Even if the positions are beyond the Galactic center, the radio supernova could be observed using middle size radio telescope.

Intense radio sources at 1400 MHz. 11. Additions to the BDFL sample .

Sixteen sources with 1.4-0Hz integrated flux densities greater than 1.7 Jy and Ib >5' have been added to the 424 in the BDFL catalog (Paper I) between declinations -5' and +70', on the evidence of new 1.4-0Hz observations at the NRAO 300-ft telescope. The BDFL "complete sample" of sources with S lA >2.00 Jy in the region of sky between declinations -5' and 70' at Ib 1>20' has consequently been slightly revised. Five new sources have been added and two sources deleted. The revised BDFL "complete" sample of 237 sources (Table V of this paper) is estimated to be 99:1:1% complete. Data on the additional sources are given in Table II of this paper, which also presents new data on 14 sources from the BDFL catalog. All sources with 1.4-0Hz flux densities greater than 1.5 Jy in the Ohio 40' 3' survey at jb I>5' have now been observed at the 300-ft telescope, and the flux-density accuracy of this survey is assessed.

An Interferometric Survey of the Areas Surrounding Four Intense Radio Sources

WE report here the results of an interferometric survey of the areas surrounding the intense radio sources Cassiopeia A, Cygnus A, Taurus A and Virgo A. These areas have remained unsurveyed because with most techniques the intense sources produce sidelobe responses which completely obscure any weaker ones surrounding them. Even with the aperture synthesis methods used in the 4C survey1 the grating responses obscure areas of several square degrees around the intense sources. The present search was conducted with a long baseline radio link interferometer which has the advantage that the sidelobe responses are reduced by several orders of magnitude because the intense sources are well resolved. This point is illustrated by Table 1 which lists the 408 MHz flux densities of the four intense sources together with the typical apparent flux densities as seen by the Jodrell Bank Mk III interferometer (32,000 wavelengths at 408 MHz).

Flux densities, positions, and structures for a complete sample of intense radio sources at 1400 MHz.

Flux densities, positions, and structures for a complete sample of intense radio sources at 1400 MHz.

Counts of Intense Extragalactic Radio Sources at 1,400 MHz

1,400 MHz extragalactic radio source counts indicate that the exponent of the relation between number and flux density is only greater than 1.5 at very low source densities.

Observations of Intense Radio Sources with a 1'5 Fan Beam

view Abstract Citations (2) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Intense Radio Sources with a 1'5 Fan Beam Legg, T. H. ; Bell, M. B. ; Bignell, R. C. Abstract The right ascension and east-west structure of seven intense radio sources have been determined at 10.7 cm using an antenna array with a 1,5 fan beam. The sources observed were Tau A, the Orion nebula, 3C273, Cyg A, Cas A, and the Omega nebula. Many observations of the moon were made concurrently in the hope of reducing systematic error by relating the lunar transit to the transit of the sources. Standard errors in right ascensions range from 0.16 to 0.58 and agreement as good or better than the standard error is found with the results of Fomalont (1968) at 21 cm, suggesting that there is no strong dependence of position upon wavelength. Some structural features are resolved for all sources except 3C273: the main sources in the Orion and Omega nebulas apparently remain asymmetrical when the secondary sources are accounted for; the peak emission from Vir A is more closely associated with the nucleus than the jet, with the halo component contributing approximately 28% of the total flux; and the third source in Cyg A con- tributes an estimated 10% of the total flux. Publication: The Astronomical Journal Pub Date: November 1968 DOI: 10.1086/110693 Bibcode: 1968AJ.....73..749L full text sources ADS | data products NED (6)

γ-rays from discrete radio sources

The fluxes of low energy (∼100 MeV) and high energy (∼5×1012 eV)γ-rays from intense radio sources have been calculated under the hypothesis that radio electrons are continuously produced through nuclear collisions. The effect of expansion of the source which gives rise to a decrease in production rate with time has been taken into account in these calculations. It is found that the fluxes expected from nuclear collision process are generally higher than the fluxes from other processes like bremstrahlung and inverse compton scattering by factors of 10 or more. While the calculated fluxes ofγ-rays of energy >100 MeV are less than the observed upper limits for all the processes, the fluxes calculated for nuclear collision process for E>5×1012 eV, exceed the experimental upper limits for Crab, Cas A and the jet in Virgo A. More sensitive experiments should be able to decide whether the nuclear collision process is ruled out for low energies as well: in this respect Cas A seems to be the most promising source.

Radio Emission from the Nucleus of the Andromeda Nebula

Sagittarius A, the intense radio source at the centre of our Galaxy, has no counterpart in the Andromeda Nebula although the structure of the nucleus is otherwise similar. The bright supernova of 1885 in Andromeda produces far less radio emission than would be expected from a comparison with remnants of galactic supernovae.

Observations of the Six Most Intense Radio Sources with a 1.0' Fan Beam.

Observations of the Six Most Intense Radio Sources with a 1.0' Fan Beam.

Tests for Linear Polarization in the 1390 Mc/s. Radiation from Six Intense Radio Sources.

The 1390 Mc/s radiation from six intense sources was examined for linear polarization. Of the six sources investigated, two were emission nebulae, two were remnants of galactic supernovae, and two were extragalactic double sources. A polarized component of 15 per cent was detected in the radiation from the Crab Nebula, and upper limits were set for the polarization of the remaining five sources.

Star Formation in Elliptical Galaxies and Intense Radio Sources

CAMERON1 considers that the mechanism which I have proposed to explain radio emission from elliptical galaxies2 is implausible. Since I have been looking into this question rather carefully, I do not agree; but the discussion of this problem is of great complexity and nothing can be gained by making general assertions. Let us concentrate therefore on a discussion of the mechanism of energy generation put forward in Cameron's communication with the view of deciding whether it provides a reasonable alternative to the mechanism proposed by me.

Star Formation in Elliptical Galaxies and Intense Radio Sources

G. R. BURBIDGE has recently reviewed the problem of the energy sources required to give the non-thermal radio emission from intense extragalactic sources1. The intrinsically strongest sources appear to be mostly associated with giant elliptical galaxies, and to be radiating at power-levels up to 107 times that of our own Galaxy. Burbidge argues convincingly that the high-energy particles responsible for the radio emission must be accelerated in supernova explosions. A typical strong radio source would require the explosion of 107 or 108 supernovae in a period of 107 or 108 years. This is a considerably greater supernova-rate than normally occurs in a galaxy.

Star Formation in Elliptical Galaxies and Intense Radio Sources.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Star Formation in Elliptical Galaxies and Intense Radio Sources. Cameron, A. G. W. Abstract Burbidge, the most probable energy input to intense radio emission comes from a short-lived period of enhanced supernova activity in a galaxy; he suggested that a Type I supernova chain reaction might accomplish this. I consider the former proposal convincing, but the latter suggestion implausible. Instead, it appears probable that in a giant elliptical galaxy, a type most commonly associated with intense radio sources, star formation should inevitably lead to a short-lived period of intense Type II supernova activity. If a hydrogen number density ~0.01 cm-3 and a magnetic field 10-6 gauss are not untypical of such galaxies, then, from the virial theorem, it follows that gravitational instability will arise only when the gravitational potential energy is greater than the magnetic energy contained in a large mass of gas (108 or more solar masses). In the ensuing collapse of such a gas cloud, the rise of the magnetic field energy prevents fragmentation; the collapse should continue until a flattened disk is formed. Star formation can then probably take place in a few million years by condensation along the lines of force. We do not know what luminosity function to expect for the new stars; the formation of small stars may be inhibited by the large magnetic field. The massive stars should all evolve to the Type II supernova stage in about three million years. The condensation process always produces a pinch in the magnetic field, and should occasionally produce an optical j et such as that of M87. If the magnetic field has intergalactic connections, then the field expansion caused by the high energy density of the particles should produce two outward-moving magnetic mirrors, and hence a double radio source. Publication: The Astronomical Journal Pub Date: March 1962 DOI: 10.1086/108815 Bibcode: 1962AJ.....67Q.269C full text sources ADS |

Cosmological Significance of Angular Measurements of Distant Radio Sources

THE programme of interferometric observations of distant radio sources at present being carried out by H. P. Palmer et al. at Jodrell Bank may prove to be of great significance for cosmology. The preliminary results recently published1 indicate that out of 91 sources 38 were of sufficiently small angular diameter to produce measurable interference fringes at the long base line used (32,000 λ at λ = 1.89 m.), and at least 7 had a diameter between half-power points less than 3 sec. of arc. Furthermore, these 7 were described as having “an extremely high surface brightness which is comparable with that of the intense radio source in Cygnus I.A.U. 19 N4A”.

The accurate positions of 17 intense radio sources

Observations of 17 intense sources were made at a 1.9-meter wavelength with the Cambridge four-aerial interferometer [1] to provide information that may assist in their identification with optical objects, and as a check on the positions of a few of the sources of the recently completed third Cambridge survey [2].

V. The measurement of the angular diameter of two intense radio sources. I: A radio interferometer using post-detector correlation

Abstract A description of a practical interferometer system based on the principle of post-detector correlation is followed by a short account of an instrument incorporating this principle. This instrument has been used at Jodrell Bank for measurements of the angular diameters and structures of the radiation from the quiet sun and the sources Cygnus and Cassiopeia. The method of computing the results is indicated, and a short account is given of a synthetic source which is used to calibrate the equipment. Reference is made to a method of obtaining the gradient of the correlation function by the use of three adjacent operating frequencies. The results of the measurements on Cassiopeia and Cygnus are given in Part II of this paper.

Polarization Measurements on Three Intense Radio Sources

Polarization Measurements on Three Intense Radio Sources

The spatial distribution and the nature of radio stars

An investigation of the number-intensity distribution of the observed radio stars shows that they cannot be interpreted in terms of a homogeneous distribution of sources; there is an apparent increase in the spatial density or absolute luminosity of distant sources. It is also found that this increase is, within rather small statistical errors, independent of direction. It therefore appears that the solar system is situated at the centre of a spherical region in which the spatial density or luminosity of the sources increases with distance, uniformly in all directions. It may also be concluded that this increase does not persist for distances much greater than those to which sources have been observed individually. It appears impossible to explain the results in terms of sources situated within the galaxy, or by irregular clustering of extra-galactic sources. Furthermore, it may be shown from arguments based on the integrated radiation that the minimum radius of the spherical region is comparable with that of the optically observable universe. It is therefore suggested that the observed features are due to effects on a cosmical scale; such an explanation provides an immediate reason for the remarkably isotropic distribution of radio stars. Attempts to explain the observations according to steady-state theories offer little hope of success, but there seems every reason to suppose that they might be explained in terms of an evolutionary theory. No detailed comparison has yet been made between the observations and the predictions of any particular evolutionary model, but a general explanation of the observations seems possible if it is supposed that the majority of radio stars belong to an excessively rare class of object, having a local spatial density of about 2 x 10 -26 parsec -3 , and an absolute luminosity comparable with that of the intense radio source in Cygnus. On this interpretation, the difficulty of identifying radio stars with optical objects finds a natural explanation; only some tens of the main class of radio star would be within reach of the 200 in. telescope.

Radio-Frequency Radiation from the Rosette Nebula

A RECENT radio survey of the galactic anti-centre region, made at 242 Mc./s. with the Ohio State University radio telescope, has revealed an intense extended radio source in the constellation of Monoceros. The co-ordinates of the radio source agree closely with the position of the Rosette nebula surrounding the galactic cluster NGC2244. Also the width in right ascension of the radio source is comparable with the diameter of the nebula. Thus, it is presumed that the radio source may be identified with the Rosette nebula.