1997/10/14 by Insu Yi, Yi, Insu, S. P. Boughn +2
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics (astro-ph) #Astrophysics and Cosmic Phenomena #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9710147
16 pages, 2 figures, ApJ
arxiv created 1997/10/14 · openalex publication_date 1997/10/14 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
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× 1035(ν/15GHz)7/5(M/107M\odot) (Lx/1040 erg s-1)1/10 erg s-1 where LR=νLν is the radio luminosity at frequency ν, M is the mass of the accreting black hole, and 1040 \simle Lx\simle 1042 erg s-1 is the 2-10 keV X-ray luminosity. These sources are characterized by inverted radio spectra Iν∝ ν2/5. For example, an ADAF X-ray source with luminosity Lx∼ 1041 erg s-1 has a nuclear radio luminosity of ∼ 4× 1036(M/3× 107M\odot) erg s-1 at ∼ 20 GHz and if at a distance of ∼ 10 (M/3× 107M\odot)1/2 Mpc would be detected as a ∼ 1mJy 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.