Using infrared/X-ray flare statistics to probe the emission regions near the event horizon of Sgr A*

TL;DR

This study analyzes infrared and X-ray flare statistics from Sgr A* to understand the emission regions near the black hole's event horizon, using models that incorporate parameter fluctuations to match observed flux distributions.

Contribution

It introduces a statistical modeling approach for flare flux distributions considering parameter fluctuations, distinguishing between synchrotron and SSC emission scenarios.

Findings

Fluctuations in particle acceleration power dominate flare variability.

Synchrotron model constrains acceleration slope fluctuations for brightest flares.

SSC model constrains magnetic field and density variation distributions.

Abstract

The supermassive black hole at the centre of the Galaxy flares at least daily in the infrared (IR) and X-ray bands, yet the process driving these flares is still unknown. So far detailed analysis has only been performed on a few bright flares. In particular, the broadband spectral modelling suffers from a strong lack of simultaneous data. However, new monitoring campaigns now provide data on thousands of flaring events, allowing a statistical analysis of the flare properties. In this paper, we investigate the X-ray and IR flux distributions of the flare events. Using a self-consistent calculation of the particle distribution, we model the statistical properties of the flares. Based on a previous work on single flares, we consider two families of models: pure synchrotron models and synchrotron self-Compton (SSC) models. We investigate the effect of fluctuations in some relevant parameters (e.g. acceleration properties, density, magnetic field) on the flux distributions. The distribution of these parameters is readily derived from the flux distributions observed at different wavelengths. In both scenarios, we find that fluctuations of the power injected in accelerated particles plays a major role. This must be distributed as a power-law (with different indices in each model). In the synchrotron dominated scenario, we derive the most extreme values of the acceleration power required to reproduce the brightest flares. In that model, the distribution of the acceleration slope fluctuations is constrained and in the SSC scenario we constrain the distributions of the correlated magnetic field and flow density variations.