2,254,595 research outputs found

    Radio Variability of Radio Quiet and Radio Loud Quasars

    Full text link
    The majority of quasars are weak in their radio emission, with flux densities comparable to those in the optical, and energies far lower. A small fraction, about 10%, are hundreds to thousands of times stronger in the radio. Conventional wisdom holds that there are two classes of quasars, the radio quiets and radio louds, with a deficit of sources having intermediate power. Are there really two separate populations, and if so, is the physics of the radio emission fundamentally different between them? This paper addresses the second question, through a study of radio variability across the full range of radio power, from quiet to loud. The basic findings are that the root mean square amplitude of variability is independent of radio luminosity or radio-to-optical flux density ratio, and that fractionally large variations can occur on timescales of months or less in both radio quiet and radio loud quasars. Combining this with similarities in other indicators, such as radio spectral index and the presence of VLBI-scale components, leads to the suggestion that the physics of radio emission in the inner regions of all quasars is essentially the same, involving a compact, partially opaque core together with a beamed jet.Comment: 32 pages, 9 figures. Astrophysical Journal, in pres

    The radio luminosity, black hole mass and Eddington ratio for quasars from the Sloan Digital Sky Survey

    Full text link
    We investigate the \mbh- \sigma_* relation for radio-loud quasars with redshift z<0.83z<0.83 in Data Release 3 of the Sloan Digital Sky Survey (SDSS). The sample consists of 3772 quasars with better model of Hő≤\beta and \oiii lines and available radio luminosity, including 306 radio-loud quasars, 3466 radio-quiet quasars with measured radio luminosity or upper-limit of radio luminosity (181 radio-quiet quasars with measured radio luminosity). The virial supermassive black hole mass (\mbh) is calculated from the broad \hb line, the host stellar velocity dispersion (ŌÉ‚ąó\sigma_*) is traced by the core \oiii gaseous velocity dispersion, and the radio luminosity and the radio loudness are derived from the FIRST catalog. Our results are follows: (1) For radio-quiet quasars, we confirm that there is no obvious deviation from the \mbh- \sigma_* relation defined in inactive galaxies when \mbh uncertainties and luminosity bias are concerned. (2) We find that radio-loud quasars deviate much from the \mbh- \sigma_* relation respect to that for radio-quiet quasars. This deviation is only partly due to the possible cosmology evolution of the \mbh- \sigma_* relation and the luminosity bias. (3) The radio luminosity is proportional to \mbh^{1.28^{+0.23}_{-0.16}}(\lb/\ledd)^{1.29^{+0.31}_{-0.24}} for radio-quiet quasars and \mbh^{3.10^{+0.60}_{-0.70}}(\lb/\ledd)^{4.18^{+1.40}_{-1.10}} for radio-loud quasars. The weaker correlation of the radio luminosity dependence upon the mass and the Eddington ratio for radio-loud quasars shows that other physical effects would account for their radio luminosities, such as the black hole spin.Comment: 15 pages, 8 figures, 2 tables, accepted for publication in ChJA

    ATMOSPHERIC GASES ATTENUATION IN WEST AFRICA

    Get PDF
    Atmospheric gases variations were evaluated to have major effect on Ku-band and above at 0.01 % unavailability of an average year on both uplink and down link. The International Telecommunication Union Radio Propagation Recommendation (ITU-RP 676, 2012) data bank was used for the computation of gaseous attenuation for West Africa. Monthly and yearly mean of temperature, pressure and relative humidity were used as input parameters obtained from ITU-R study group 3 data base. The results presented on contour map show that total atmospheric absorption signal fade attenuation values at C, Ku, Ka and V bands is between 0.015 to 0.09 dB, 0.04 to 0.9 dB, 0.04 to 1.4 dB and 0.2 to 3.2 dB respectively for both uplink and downlink frequencies. Generally, consistent signal absorption due to Oxygen and water vapour are higher in the western region than southern part of West Africa

    Radio

    Get PDF

    Radio-Excess IRAS Galaxies: IV. Optical Spectroscopy

    Get PDF
    This is the fourth in our series of papers investigating radio-excess galaxies, which have radio emission associated with an active nucleus but which do not fit into the traditional categories of either radio-loud or radio-quiet active galaxies. In this paper, we present optical spectra of our sample of FIR-luminous radio-excess galaxies. Optical emission line diagnostics are used to determine the dominant source of the ionizing radiation. We find that radio excess is an excellent indicator of the presence of an active nucleus: the radio-excess sample contains a much higher fraction of AGN than samples selected on FIR luminosity alone, or using other criteria such as warm FIR colors. Several objects have ambiguous classifications and are likely to be composite objects with mixed excitation. The type of optical spectrum appears to be associated with the radio-loudness: radio-loud objects may be more `pure' AGN than radio-intermediate objects. We find strong evidence for interaction between the radio plasma and the surrounding gas. The jet energy fluxes of the radio-excess objects, inferred from the [O III] luminosities, are lower than in powerful radio sources, consistent with our previous results. We conclude that the jets of radio-intermediate sources are intrinsically weaker than those in sources with more powerful radio emission. A significant fraction of the sample spectra show post-starburst stellar continuum, with A-star absorption lines, consistent with the large fraction of merging or disturbed host galaxies in the sample. The ages of the radio sources are significantly less than those of A stars indicating that, if the radio sources are associated with merging activity, there is a delay between the interaction and the initiation of the radio activity. (Abridged.)Comment: Accepted for publication in AJ; version with high resolution figures available from http://www.cis.rit.edu/~clbsps/papers/paper4.pd

    The Dynamics of Radio Galaxies and Double-Double Radio Galaxies

    Full text link
    Relativistic and magnetised plasma ejected by radio loud AGNs through jets form the diffuse lobes of radio galaxies. The radiating particles (electron/electron-positron) in lobes emit in radio via the synchrotron process and X-ray via inverse-Compton scattering of cosmic microwave background photons. The thermal environment around radio galaxies emits X-rays via the thermal bremsstrahlung process. By combining information from these processes we can measure physical conditions in and around the radio lobes and thus study the dynamics of radio galaxies, including double-double radio galaxies.Comment: 11 pages, 4 figures, Diffuse Radio Plasma Conference proceedings (held in Raman Research Institute, Bangalore, India

    Radio and spectroscopic properties of miniature radio galaxies: revealing the bulk of the radio-loud AGN population

    Full text link
    We explore radio and spectroscopic properties of a sample of 14 miniature radio galaxies, i.e. early-type core galaxies hosting radio-loud AGN of extremely low radio power, 10^(27-29) erg s^(-1) Hz^(-1) at 1.4 GHz. Miniature radio galaxies smoothly extend the relationships found for the more powerful FRI radio galaxies between emission line, optical and radio nuclear luminosities to lower levels. However, they have a deficit of a factor of ~100 in extended radio emission with respect to that of the classical example of 3CR/FRI. This is not due to their low luminosity, since we found radio galaxies of higher radio core power, similar to those of 3CR/FRI, showing the same behavior, i.e. lacking significant extended radio emission. Such sources form the bulk of the population of radio-loud AGN in the Sloan Digital Sky Survey. At a given level of nuclear emission, one can find radio sources with an extremely wide range, a factor of >~100, of radio power. We argue that the prevalence of sources with luminous extended radio structures in flux limited samples is due to a selection bias, since the inclusion of such objects is highly favored. The most studied catalogues of radio galaxies are thus composed by the minority of radio-loud AGN that meet the physical conditions required to form extended radio sources, while the bulk of the population is virtually unexplored.Comment: 15 pages. Accepted for publication in A&
    • ‚Ķ
    corecore