Accretion of Matter and Emission Spectra of Binary X-ray Sources in Massive Brans-Dicke Gravity

Abstract

We study accretion of matter as well as X-ray emission spectra of low-mass black hole binaries in massive Brans-Dicke gravity assuming that the gravitational field generated by the stellar-mass black hole in the binary is the Schwarzschild-de Sitter space-time, which is the analogue of the Schwarzschild geometry of Einstein’s theory in massive Brans-Dicke gravity. In the first part of the computation we compute the accretion disk surrounding the stellar mass black hole adopting the well-known non-relativistic Shakura-Sunyaev model for an optically thick, cool, and geometrically thin disk. The most relevant quantities of interest are computed, i.e., i) the fluid radial velocity, ii) the energy and surface density, and iii) the pressure as a function of the radial coordinate. Next, in the second part of the computation we compute the soft spectral component of the X-ray emission expected from the disk. Finally, we investigate in detail the impact of the mass of the scalar field on the properties of the binary, and we make a comparison to the usual Schwarzschild solution as well.