Source-intrinsic near-infrared properties of Sgr A*: Total intensity measurements

TL;DR

This paper analyzes Ks-band near-infrared measurements of Sgr A*, revealing a power-law flux distribution, a linear rms-flux relation, and discussing the limitations of current data in resolving variability structures at certain timescales.

Contribution

It provides a detailed statistical characterization of Sgr A*'s near-infrared variability and introduces a phenomenological model to simulate and extrapolate its behavior.

Findings

Flux density follows a power-law distribution.

Linear rms-flux relation up to 12 mJy.

Data cadence limits detection of structure at 25-100 min timescales.

Abstract

We present a comprehensive data description for Ks-band measurements of Sgr A*. We characterize the statistical properties of the variability of Sgr A* in the near-infrared, which we find to be consistent with a single-state process forming a power-law distribution of the flux density. We discover a linear rms-flux relation for the flux-density range up to 12 mJy on a timescale of 24 minutes. This and the power-law flux density distribution implies a phenomenological, formally non-linear statistical variability model with which we can simulate the observed variability and extrapolate its behavior to higher flux levels and longer timescales. We present reasons why data with our cadence cannot be used to decide on the question whether the power spectral density of the underlying random process shows more structure at timescales between 25 min and 100 min compared to what is expected from a red noise random process.