Flare emission from Sagittarius A*

TL;DR

This paper models the multi-wavelength flaring activity of Sagittarius A* using synchrotron and SSC mechanisms, revealing insights into the physical conditions and dynamics near the supermassive black hole.

Contribution

It introduces a comprehensive model combining synchrotron and SSC processes to explain SgrA*'s variability across radio, infrared, and X-ray bands, with detailed parameter analysis.

Findings

Flaring activity can be modeled as adiabatically expanding synchrotron self-Compton components.

Synchrotron turnover frequencies are typically 300-400 GHz, with relativistic particle densities around 10^6.5 cm^-3.

Models require higher turnover frequencies and densities to match observed variability amplitudes.

Abstract

Based on Bremer et al. (2011) and Eckart et al. (2012) we report on simultaneous observations and modeling of the millimeter, near-infrared, and X-ray flare emission of the source Sagittarius A* (SgrA*) associated with the super-massive black hole at the Galactic Center. We study physical processes giving rise to the variable emission of SgrA* from the radio to the X-ray domain. To explain the statistics of the observed variability of the (sub-)mm spectrum of SgrA*, we use a sample of simultaneous NIR/X-ray flare peaks and model the flares using a synchrotron and SSC mechanism. The observations reveal flaring activity in all wavelength bands that can be modeled as the signal from adiabatically expanding synchrotron self-Compton (SSC) components. The model parameters suggest that either the adiabatically expanding source components have a bulk motion larger than v_exp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*. For the bulk of the synchrotron and SSC models, we find synchrotron turnover frequencies in the range 300-400 GHz. For the pure synchrotron models this results in densities of relativistic particles of the order of 10^6.5 cm^-3 and for the SSC models, the median densities are about one order of magnitude higher. However, to obtain a realistic description of the frequency-dependent variability amplitude of SgrA*, models with higher turnover frequencies and even higher densities are required. We discuss the results in the framework of possible deviations from equilibrium between particle and magnetic field energy. We also summarize alternative models to explain the broad-band variability of SgrA*.