General relativistic effects and the near-infrared variability of Sgr A*. II. A systematic approach to temporal asymmetry

Abstract

A systematic study, based on the third-moment structure function, of Sgr A*'s variability finds an exponential rise time, $ obs minutes $, and decay time, $ obs minutes $. This symmetry of the flux-density variability is consistent with earlier work, and we interpret it as being caused by the dominance of Doppler boosting, as opposed to gravitational lensing, in Sgr A*'s light curve. A relativistic, semi-physical model of Sgr A* confirms an inclination angle of $i The model also shows that the emission of the intrinsic radiative process can have some asymmetry even though the observed emission does not. The third-moment structure function, which is a measure of the skewness of the light-curve increments, may be a useful summary statistic in other contexts of astronomy because it senses only temporal asymmetry; that is, it averages to zero for any temporally symmetric signal.