Physics
Scientific paper
May 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...499..198y&link_type=abstract
Astrophysical Journal v.499, p.198
Physics
39
Accretion, Accretion Disks, Black Hole Physics, Galaxies: Nuclei, Radiation Mechanisms: Nonthermal, Radio Continuum: Galaxies, X-Rays: Galaxies
Scientific paper
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 LR ~ 7 x 1035( nu /15 GHz)7/5(M/107 M&sun;)(LX/1040 ergs s-1)1/10 ergs s-1, where LR = nu L nu is the radio luminosity at frequency nu , M is the mass of the accreting black hole, and 1040 <~ LX <~ 1042 ergs s-1 is the 2-10 keV X-ray luminosity. These sources are characterized by inverted radio spectra I nu ~ nu 2/5. For example, an ADAF X-ray source with luminosity LX ~ 1041 ergs s-1 has a nuclear radio luminosity of ~4 x 1036(M/3 x 107 M&sun;) ergs s-1 at ~20 GHz, and if it is at a distance of ~10(M/3 x 107 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.
Boughn Stephen P.
Yi Insu
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