  General Relativity predicts the spacetime metric around an astrophysical
black hole to be described by Kerr solution which is a massive rotating black
hole without any residual charge. In a previous paper, we analyzed the NuSTAR
observations of six X-ray binaries to obtain constraints on deformation
parameter $\alpha_{13}$ using a state-of-the-art relativistic model. In this
work, we continue analyzing NuSTAR observations of four more X-ray Binaries;
two of which are X-ray Transients very close to the supermassive black hole at
the center of our galaxy. The other two sources have complicated absorption
which is accounted by time-resolved and flux-resolved spectroscopy. The
constraints obtained are consistent with the Kerr hypothesis and are comparable
with those obtained in previous studies and those from gravitational events.
