Accretion disc evolution in GRO J1655-40 and LMC X-3 with relativistic and non-relativistic disc models
Abstract
Black hole X-ray binaries are ideal environments to study the accretion phenomena in strong gravitational potentials. These systems undergo dramatic accretion state transitions and analysis of the X-ray spectra is used to probe the properties of the accretion disc and its evolution.
In this work, we present a systematic investigation of & SIM;1800 spectra obtained by Rossi X-Ray Timing Explorer Proportional Counter Array observations of GRO J1655-40 and LMC X-3 to explore the nature of the accretion disc via non-relativistic and relativistic disc models describing the thermal emission in black hole X-ray binaries. We demonstrate that the non-relativistic modelling throughout an outburst with the phenomenological multicolour disc model DISKBB yields significantly lower and often unphysical inner disc radii and correspondingly higher (& SIM;50-60 per cent) disc temperatures compared to its relativistic counterparts KYNBB and KERRBB.
We obtained the dimensionless spin parameters of a(*) = 0.774 & PLUSMN; 0.069 and a(*) = 0.752 & PLUSMN; 0.061 for GRO J1655-40 with KERRBB and KYNBB, respectively. We report a spin value of a(*) = 0.098 & PLUSMN; 0.063 for LMC X-3 using the updated black hole mass of 6.98 M-& ODOT;.
Both measurements are consistent with the previous studies. Using our results, we highlight the importance of self-consistent modelling of the thermal emission, especially when estimating the spin with the continuum-fitting method which assumes the disc terminates at the innermost stable circular orbit at all times.