共查询到20条相似文献，搜索用时 46 毫秒
1.
V. L. Afanasiev S. N. Dodonov A. V. Moiseev V. Chavushyan R. Mujica Y. Juarez A. G. Gorshkov V. K. Konnikova M. G. Mingaliev 《Astronomy Letters》2003,29(9):579-586
We present the classification of optical identifications and radio spectra of six radio sources from a complete (in flux density) sample in the declination range 10° to 12°30′ (J2000.0). The observations were carried out with the 6-m Special Astrophysical Observatory telescope (Russia) in the wavelength range 3600–10000 Å, the 2.1-m GHAO telescope (Mexico) in the range 4200–9000 Å, and the RATAN-600 radio telescope in the frequency range 0.97–21.7 GHz. Three of the six objects under study are classified as quasars, one is a BL Lac object, one is an absorption-line radio galaxy, and one is an emission-line radio galaxy. Five objects have flat radio spectra, and one object has a power-law radio spectrum. All of the radio sources identified as quasars or BL Lac objects show variable radio flux densities. The spectra of three objects were separated into extended and compact components. 相似文献
2.
M. A. Hovhannissian 《Astrophysics》1995,38(4):389-389
Published in Astrofizika, Vol. 38, No. 4, pp. 692–693, October–December, 1995. 相似文献
3.
Radio astronomy has changed. For years it studied relatively rare sources, which emit mostly non-thermal radiation across the entire electromagnetic spectrum, i.e. radio quasars and radio galaxies. Now, it is reaching such faint flux densities that it detects mainly star-forming galaxies and the more common radio-quiet active galactic nuclei. These sources make up the bulk of the extragalactic sky, which has been studied for decades in the infrared, optical, and X-ray bands. I follow the transformation of radio astronomy by reviewing the main components of the radio sky at the bright and faint ends, the issue of their proper classification, their number counts, luminosity functions, and evolution. The overall “big picture” astrophysical implications of these results, and their relevance for a number of hot topics in extragalactic astronomy, are also discussed. The future prospects of the faint radio sky are very bright, as we will soon be flooded with survey data. This review should be useful to all extragalactic astronomers, irrespective of their favourite electromagnetic band(s), and even stellar astronomers might find it somewhat gratifying. 相似文献
4.
C. H. Ishwara-Chandra D. J. Saikia P. J. McCarthy W. J. M. van Breugel 《Monthly notices of the Royal Astronomical Society》2001,323(2):460-470
We present multi-wavelength radio observations with the Very Large Array, and narrow- and broad-band optical observations with the 2.5-m telescope at the Las Campanas Observatory, of a well-defined sample of high-luminosity Fanaroff–Riley class II radio galaxies and quasars, selected from the Molonglo Reference Catalogue 1-Jy sample. These observations were carried out as part of a programme to investigate the effects of orientation and environment on some of the observed properties of these sources. We examine the dependence of the Liu–Pooley relationship, which shows that radio lobes with flatter radio spectra are less depolarized, on size, identification and redshift, and show that it is significantly stronger for smaller sources, with the strength of the relationship being similar for both radio galaxies and quasars. In addition to Doppler effects, there appear to be intrinsic differences between the lobes on opposite sides. We discuss the asymmetry in brightness and location of the hotspots, and present estimates of the ages and velocities from matched-resolution observations in the L and C bands. Narrow- and broad-band optical images of some of these sources were made to study their environments and correlate with the symmetry parameters. An extended emission-line region is seen in a quasar, and in four of the objects possible companion galaxies are seen close to the radio axis. 相似文献
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6.
We propose an explanation of the origin of the central radio gaps which are usually observed in extragalactic radio sources that exhibit jet structures.An estimate was made of neutron Lorentz factors of neutrons responsible for energy transport from the central engine of active galactic nuclei (AGNs) to the jet turn-on point of typical AGNs.The probable explanations of the existence of different belts in the radio gap morphology was attempted. 相似文献
7.
G. S. Sahakian 《Astrophysics》2000,43(1):111-126
The theory of pulsar radio emission has been developed in a series of our papers since 1992. It was shown that pulsar radio
emission is produced in the lower part of a channel of open magnetic field lines, in a region with a height h ≈ 1.1-107 μ
30
1/3
/P4/21 cm above a magnetic cap of the neutron star (P is the pulsar’s period and μ is the star’s magnetic moment). Here, owing to
vigorously occurring processes (the production of photons of curvature radiation and their annihilation into e+e- pairs), two ultrarelativistic particle fluxes are formed: an electron flux moving upward and a positron flux falling onto
the star’s magnetic cap. These main fluxes are accompanied by narrow strips of positron and electron fluxes of relatively
low energy, the curvature emission from which is a strong coherent radio source. The present paper is a review of earlier
papers, and important additions and refinements are also made. Equations are offered for the radio luminosity of a pulsar,
the solid angle of the radio beam, and the magnetic moment and moment of inertia of the pulsar’s neutron star.
Translated from Astrofizika, Vol. 43, No. 1, pp. 147-169, January–March, 2000. 相似文献
8.
W. C. Erickson 《Journal of Astrophysics and Astronomy》1984,5(1):55-65
Ionospheric refraction effects encountered in radio source observations in the 30 to 75 MHz range with the Clark Lake TPT
telescope are discussed. It is found that simple calibration procedures are sufficient to provide positions of unknown sources
with an accuracy of approximately one arcmin. Observations made near sunrise, or during disturbed ionospheric conditions must
be discarded. If no corrections are applied, RMS errors of a few arcmin are to be expected.
On leave at Radiosterrenwacht Dwingeloo, The Netherlands 相似文献
9.
Fast Radio Bursts (FRBs) are short duration highly energetic dispersed radio pulses. We developed a generic formalism (Bera et al. 2016, MNRAS, 457, 2530) to estimate the FRB detection rate for any radio telescope with given parameters. By using this model, we estimated the FRB detection rate for two Indian radio telescope; the Ooty Wide Field Array (OWFA) (Bhattacharyya et al. 2017, J. Astrophys. Astr., 38, 17) and the upgraded Giant Metrewave Radio Telescope (uGMRT) (Bhattacharyya et al. 2018, J. Astrophys. Astr.) with three beam-forming modes. Here, we summarize these two works. We considered the energy spectrum of FRBs as a power law and the energy distribution of FRBs as a Dirac delta function and a Schechter luminosity function. We also considered two scattering models proposed by Bhat et al. (2004, Astrophys. J. Suppl. Series, 206, 1) and Macquart & Koay (2013, ApJ, 776, 125) for these works and we consider FRB pulse without scattering as a special case. We found that the future prospects of detecting FRBs by using these two Indian radio telescopes is good. They are capable to detect a significant number of FRBs per day. According to our prediction, we can detect \(\sim 10^5{-}10^8\), \(\sim 10^3{-}10^6\) and \(\sim 10^5{-}10^7\) FRBs per day by using OWFA, commensal systems of GMRT and uGMRT respectively. Even a non detection of the predicted events will be very useful in constraining FRB properties. 相似文献
10.
C. H. Ishwara-Chandra D. J. Saikia 《Monthly notices of the Royal Astronomical Society》1999,309(1):100-112
We present multifrequency Very Large Array (VLA) observations of two giant quasars, 0437−244 and 1025−229, from the Molonglo Complete Sample. These sources have well-defined FR II radio structure, possible one-sided jets, no significant depolarization between 1365 and 4935 MHz and low rotation measure (|RM|<20 rad m−2 ). The giant sources are defined to be those with overall projected size 1 Mpc. We have compiled a sample of about 50 known giant radio sources from the literature, and have compared some of their properties with a complete sample of 3CR radio sources of smaller sizes to investigate the evolution of giant sources, and test their consistency with the unified scheme for radio galaxies and quasars. We find an inverse correlation between the degree of core prominence and total radio luminosity, and show that the giant radio sources have similar core strengths to smaller sources of similar total luminosity. Hence their large sizes are unlikely to be caused by stronger nuclear activity. The degree of collinearity of the giant sources is also similar to that of the sample of smaller sources. The luminosity–size diagram shows that the giant sources are less luminous than our sample of smaller sized 3CR sources, consistent with evolutionary scenarios in which the giants have evolved from the smaller sources, losing energy as they expand to these large dimensions. For the smaller sources, radiative losses resulting from synchrotron radiation are more significant while for the giant sources the equipartition magnetic fields are smaller and inverse Compton loss owing to microwave background radiation is the dominant process. The radio properties of the giant radio galaxies and quasars are consistent with the unified scheme. 相似文献
11.
The fluctuations of radio emission of the atmosphere (for the present only cloudy) are a substantial limiting factor for observations of cosmic radio sources on centimetre and millimetre wavelengths. For suppressing these fluctuations the dual-beam method (differential receiving from two slightly separated direction) is widely used. At the same time works for perfecting this method are going on as well as in searching other possibilities with the principal aim of doing away limitations on sizes of sources under observation. There are considered here these methods with a competitive evaluation of their possibilities for suppressing fluctuation of the atmosphere radio emissions. 相似文献
12.
Radio emission by pulsars is calculated from first principles. In an almost current-free magnetosphere, the two charged components (of the unsteadily escaping pair plasma) have different (and varying) bulk Lorentz factors. Curvature radiation emitted by the more energetic component is thus locally coherent, (so-called antenna mechanism). Strong enough seed signals cause the relativistically streaming charges to enhance their radiation, via an induced drift that can largely exceed the curvature drift. This amplification mechanism is similar to - but different from - that of a maser; we call it a MAIDER. Maximal amplification occurs at an (emission) altitude where the two components have sufficiently separated in energy though not yet separated too strongly in space. 相似文献
13.
G. S. Sahakian 《Astrophysics》1995,38(1):78-102
A new version of the theory of pulsar radio emission is developed for the case of a coaxial rotator. It is based on the electric field that we established [G. S. Sahakian, Astrofizika, 37, 97 (1994)] for the radiation channel (the channel of open magnetic field lines) and on convenient approximations for the electron energy obtained in [G. S. Sahakian and É. S. Chubarian, Astrofizika, 37, 255 (1994)]. It is shown that, owing to the emission of photons of curvature radiation by particles, e e+c', and photon annihilation, c e+e– in the lower part of the radiation channel, a special region (the magnetic funnel) is formed in which vigorous cascade multiplication of particles occurs. The height of the magnetic funnel is h 6R0.2, where R is the radius of the neutron star and is its angular rotation rate. As a result of supersaturation of the plasma density in the magnetic funnel, a discharge occurs after each time intervalt5·10–7–0.8B
12
–1.4
R
6
–0.2
, i.e., the longitudinal electric field disappears (B is the magnetic induction in the star). During the active radiative processes in the magnetic funnel, two main fluxes of particles with high ultrarelativistic energies are formed: an upward flux of electrons and a positron flux falling onto the star's magnetic cap. These fluxes are accompanied by narrow strips of positron and electron fluxes, respectively, of considerably lower energy, which are fairly powerful, coherent radio sources. The pulsar's radio luminosity is calculated to be L7.4·10223.8
30
3
R
6
–2
erg/sec, where =BR 3/2 is the star's magnetic moment. Comparing this result with observations, we conclude that the magnetic moment and hence the mass of the neutron star evidently must be considerably smaller, on the average, for fast pulsars than for slow ones. It is shown that the magnetic moment of the neutron star can be determined from the intervals between micropulses in the pulse profiles. The problem of the origin of the macrostructure of the radio pulse is discussed.Translated from Astrofizika, Vol. 38, No. 1, pp. 141–185, January – March, 1995. 相似文献
14.
Millisecond radio spikes 总被引：9，自引：0，他引：9
A. O. Benz 《Solar physics》1986,104(1):99-110
Millisecond spikes of the solar radio emission are known for more than two decades. They have recently seen a surge in interest of theoreticians who are fascinated by their high brightness temperature of up to 1015 K, their association with hard X-ray bursts, and a possibly very intimate relation to electron acceleration. This review is intended to bridge the gap that presently seems to separate theory and observations. The wide range of spike observations is summarized and brought into the perspective of recent models. It is concluded that spikes yield a considerable potential for the diagnostics of energetic particles, their origin, and history in astrophysical plasmas.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
16.
V. R. Amirkhanyan 《Astrophysical Bulletin》2016,71(4):384-394
The relation between the \(D/\sqrt I \) and IC/ISUM parameters and radiation patterns of the optical and radio components of an extended radio source is analyzed, where D and I are the apparent size and observed radiation intensity, respectively, of the source or its components. The parameters of the pattern in the optical and radio (1.4 GHz) ranges are estimated. The radiation pattern of extended radio-emitting regions is close to spherical and the radiation of the central component is concentrated in a 24? wide beam. Its luminosity is a factor of 4.58 higher than that of the extended component of the radio source. The radiation pattern of the optical component of the radio source turned out to be unexpectedly non-spherical: the main lobe of the pattern is about 26? wide. The g-band luminosity is 6.4–12.3 times higher than the luminosity of the spherical fraction of the “optical” radiation pattern. A list of 116 new giant radio sources is presented. 相似文献
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We investigate giant radio galaxy candidates that were selected based on the components cataloged as separate sources in the NVSS survey. The radio and optical identification is done for fifty radio galaxies using the CATS, NED, and SkyView databases. 相似文献
20.
Transient radio sources are necessarily compact and usually are the locations of explosive or dynamic events, therefore offering unique opportunities for probing fundamental physics and astrophysics. In addition, short-duration transients are powerful probes of intervening media owing to dispersion, scattering and Faraday rotation that modify the signals. While radio astronomy has an impressive record obtaining high time resolution, usually it is achieved in quite narrow fields of view. Consequently, the dynamic radio sky is poorly sampled, in contrast to the situation in the X-ray and γ-ray bands. The SKA has the potential to change this situation, opening up new parameter space in the search for radio transients. We summarize the wide variety of known and hypothesized radio transients and demonstrate that the SKA offers considerable power in exploring this parameter space. Requirements on the SKA to search the parameter space include the abilities to: (1) make targeted searches using beam forming capability; (2) conduct blind, all-sky surveys with dense sampling of the frequency–time plane in wide fields; (3) sample the sky with multiple fields of view from spatially well-separated sites in order to discriminate celestial and terrestrial signals; (4) utilize as much of the SKAs aggregate collecting area as possible in blind surveys, thus requiring a centrally condensed configuration, and; (5) localize repeating transient sources to high angular precision, requiring a configuration with long baselines, thus requiring collecting area in both a centrally condensed “core” array and sufficient area on long baselines. 相似文献