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Date and Time of the Query: 2019-06-25 T14:53:39 PDT
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For refcode 1998ApJ...499..198Y:
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1998ApJ...499..198Y Radio/X-Ray Luminosity Relation for Advection-dominated Accretion: Implications for Emission-Line Galaxies and the X-Ray Background INSU YI AND STEPHEN P. BOUGHN Received 1997 September 15; accepted 1998 January 1 ABSTRACT Recent studies of the cosmic X-ray background (XRB) have suggested the possible existence of a population of relatively faint sources with hard X- ray spectra; however, the emission mechanism remains unclear. If the hard X-ray emission is from the radiatively inefficient, advection-dominated accretion flows (ADAFs) around massive black holes in galactic nuclei, X- ray luminosity and radio luminosity satisfy the approximate relation L_R_~7 x 10^35^({nu}/15 GHz)^7/5^(M/10^7^ M_sun_)(L_X_/10^40^ ergs s^-1^)^1/10^ ergs s^-1^, where L_R_ = {nu}L_{nu}_ is the radio luminosity at frequency {nu}, M is the mass of the accreting black hole, and 10^40^ <~ L_X_ <~ 10^42^ ergs s^-1^ is the 2-10 keV X-ray luminosity. These sources are characterized by inverted radio spectra I_{nu}_ is proportional to {nu}^2/5^. For example, an ADAF X-ray source with luminosity L_X_ ~ 10^41^ ergs s^-1^ has a nuclear radio luminosity of ~4 x 10^36^(M/3 x 10^7^ M_sun_) ergs s^-1^ at ~20 GHz, and if it is at a distance of ~10(M/3 x 10^7^ M_sun_)^1/2^ Mpc, it would be detected as a ~1 mJy point radio source. High-frequency (~20 GHz), high angular resolution radio observations provide an important test of the ADAF emission mechanism. Since LR depends strongly on black hole mass and only weakly on X-ray luminosity, the successful measurement of nuclear radio emission could provide an estimate of black hole mass. Because the X-ray spectra produced by ADAFs are relatively hard, sources of this emission are natural candidates for contributing to the hard (>2 keV) background. Subject headings: accretion, accretion disks-black hole physics -galaxies: nuclei-radiation mechanisms: nonthermal-radio continuum: galaxies-X-rays: galaxies
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