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X-ray binaries (XRBs) often exhibit a high energy power-law tail (X-ray) andthese tails can be generated by the bulk Comptonization (BMC) process with afree-fall bulk region onto the compact object. We frequently observe a radioemission (which is generated by a synchrotron-emitting outflowing electrons)from the XRBs. We aim to study the high energy power-law tail in BMC process byan outflowing medium. We mainly consider a collimated and conical (of openingangle $\theta_b$ with axis perpendicular to the accretion disk) outflow for aBMC process. We simulate the bulk Comptonized spectra by using a Monte Carloscheme. Out of two possible conical outflow directions i) along the surface ofthe cone, ii) inside the conic region, we find that a) the randomness ofoutflow directions increases with $\theta_b$, b) the emergent spectra havepower-law tail (of photon index $\Gamma$ $>$ 2 and with high energy cut-off$E_{c}$ $>$ 200 keV) only for $\theta_b$ greater than $\sim$30 degree, whilefor a collimated or a conical outflow ($\theta_b$ $<$ 30degree) these power-lawtail can be only generated when it is also found in thermal Comptonized spectra(i.e., at sufficiently high medium temperature). We compare the GRS 1915+105spectra for two classes $\chi$ and $\gamma$, for this the outflow speed ishighly relativistic and the relevancy of wind parameters suggest that wind mustbe occurred at inner region of the accretion disk, so consistent with innerdisk radio emission.

High energy power-law tail in X-ray binaries spectrum and bulk Comptonization due to a conical outflow from a disk