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Line profiles of accretion disks around black holes in Schwarzschild-de Sitter and Einstein-Yang-Mills spacetimes Slobodov, Sergei

Abstract

We investigate the characteristic peaks in the iron line profile in the black hole accretion disk X-ray spectrum in two static spherically symmetric metrics, Schwarzschild-de Sitter metric and the Einstein-Yang-Mills black hole metric. For the Schwarzschild-de Sitter metric our results show that for a fixed mass black hole, the peaks become less pronounced and closer together with increasing cosmological constant A. This effect is mainly due to the slower rotational velocity of Keplerian orbits at large radii in the Schwarzschild-de Sitter spacetime as compared to that for the Schwarzschild spacetime. This change of the iron line profile is similar to that obtained from extending the accretion disk size or reducing the emission power law exponent in the Schwarzschild black hole accretion disk models. Based upon the current estimates of A, black holes of at least 1018 solar masses are required to make the effect observable. For Einstein-Yang-Mills black holes, the line profiles depend strongly on the horizon radius and the solution number n. For n = 1 the profile is similar to that of a Schwarzschild black hole. In contrast, the shallow slope of the g00 component of the metric for n = 2,3,4 solutions increases the line width for these solutions significantly, in some cases creating a second pair of peaks redshifted approximately by a factor of 2, breaking the usual correspondence between the position of the blue peak and the black hole mass. The line profiles of solutions for n = 5 — 8 and higher, depending on the horizon radius, closely resemble that of extreme Reissner-Nordstrom black hole. In addition, due to an island of orbit stability near the Einstein-Yang-Mills black-hole horizon for the solutions with small horizon radius r/, there is an extra pair of peaks in the line profile redshifted by a factor of 30 times or more relative to the main line. These features might be used to distinguish accreting Einstein-Yang-Mills black holes from Schwarzschild and Kerr black holes.

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