Relativistic Spectra of Hot Black-Hole Winds

TL;DR

This paper investigates the relativistic effects on the spectra emitted by hot black-hole winds, revealing how relativistic beaming and optical thinness influence observed spectral shifts and intensities.

Contribution

It provides a detailed analysis of the relativistic synchrotron spectra from spherically symmetric black-hole winds, highlighting the impact of relativistic beaming and optical depth.

Findings

Observed spectra shift to higher frequencies due to relativistic beaming.

In optically thin flows, observed intensity decreases despite frequency shifts.

Far side flows contribute to the reduced observed intensity.

Abstract

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$^*$.