Theory Meets Reality: Accretion Disc Evolution in GRO J1655-40 and LMC X-3 with Relativistic and Non-Relativistic Disc Models

Abstract

We will present a detailed investigation of X-ray spectral models used to fit the thermal accretion disk emission in black-hole X-ray binaries. We fit ~2000 RXTE observations of GRO J1655-40 and LMC X-3 to explore the nature of the accretion disk in strong gravitational fields via non-relativistic and relativistic disk models.

We find that the non-relativistic multi-color disk blackbody model (diskbb) gives significantly (about ~50-60%) higher values for disk temperatures and lower (often unphysical) inner disk radii than relativistic disk models. We find that this difference in the disk temperature and inner disk radius cannot be explained by only changing spectral hardening factor and changing inner disk radius in combination with relativistic treatment of the disk is a more probable explanation for the previously reported deviations in the L - T 4 relationship in a subset of black hole X-ray binaries.

Our study clearly shows the importance of self-consistent modeling of the thermal emission in accreting compact objects, especially when estimating the black hole spin with the continuum-fitting method.