Relativistic Spectra of Hot Black-Hole Winds

We examine hybrid thermal-nonthermal synchrotron spectra from a spherically symmetric, optically-thin wind, taking into account the relativistic effect. In the relativistic flow from the central object, due to the relativistic beaming effect, the observed spectra often shift towards high frequency and high intensity directions. In the optically thin outflows, however, we find that the intensity of the observed spectra decreases compared with that of the emitted ones, although the peak frequency shifts towards the high frequency direction. This is because in the optically thin outflows we can see the far side flows that go away from the observer. We thus carefully consider optically thin relativistic flows around a black hole such as Sgr A$^*$.