Synchrotron Self-Compton Scattering in Sgr A* Derived from NIR and X-Ray Flare Statistics

The flaring activity of Sagittarius A* (Sgr A*) can be analyzed by statistical means to test emission models for its accretion flow. A particular modeling question is whether the observed X-ray flares are the high-energy end of a synchrotron spectrum or if they arise from self-Comptonized photons of a lower-energy synchrotron process. We use already published Chandra X-ray Visionary Project data to statistically investigate the X-ray count-rate distribution of Sgr A*. Two previous workgroups have already undertaken such an analysis on that data. They modeled the flaring part of the emission with a bounded power law, i.e., a power-law distribution with a hard cutoff at the highest measured count rate. With this model, both teams obtain a power-law index a(X) similar to 2. We show that the flare count-rate distribution can also be well described by a truncated, i.e., an exponentially decaying power law. We argue that an exponential truncation is a more natural model than a hard cutoff. With this alternate model, our fit yields a power-law index alpha(X) similar to 1.66. We find that this slope can be canonically explained by a synchrotron self-Compton (SSC) process. Therefore, we argue that SSC models are the best ones suitable to explain the observed X-ray count-rate distribution.