New Simulations of the X-Ray Spectra and Polarizations of Accretion-disk Corona Systems with Various Geometrical Configurations I. Model Description

Abstract

Abstract Energetic X-ray radiations emitted from various accretion systems are widely considered to be produced by Comptonization in the hot corona. The corona and its interaction with the disk play an essential role in the evolution of the system and are potentially responsible for many observed features. However, many intrinsic properties of the corona are still poorly understood, especially for the geometrical configurations. The traditional spectral fitting method is not powerful enough to distinguish various configurations. In this paper, we intend to investigate the possible configurations by modeling the polarization properties of X-ray radiations. The geometries of the corona include the slab, sphere and cylinder. The simulations are implemented through the publicly available code, Lemon, which can deal with the polarized radiative transfer and different electron distributions readily. The results demonstrate clearly that the observed polarizations are dependent heavily on the geometry of the corona. The slab-like corona produces the highest polarization degrees (PDs), followed by the cylinder and sphere. One of the interesting things is that the PDs first increase gradually and then decrease with the increase of photon energy. For slab geometry, there exists a zero-point where the polarization vanishes and the polarization angle (PA) rotates by 90°. These results may potentially be verified by the upcoming missions for polarized X-ray observations, such as IXPE and eXTP.