Consistency of the Infrared Variability of Sgr A* over 22 years

TL;DR

This study presents a 22-year infrared variability analysis of Sgr A*, revealing consistent brightness and variability patterns, improved detection techniques, and insights into the nature of nearby objects like G1.

Contribution

It introduces enhanced speckle holography methods enabling detection of Sgr A* over a decade longer than previous studies and analyzes its long-term variability.

Findings

Sgr A* brightness and variability are consistent over 22 years.

Infrared variability follows a power-law PSD with a break at ~245 minutes.

G1's periapse had no impact on Sgr A*'s infrared emission.

Abstract

We report new infrared measurements of the supermassive black hole at the Galactic Center, Sgr A*, over a decade that was previously inaccessible at these wavelengths. This enables a variability study that addresses variability timescales that are ten times longer than earlier published studies. Sgr A* was initially detected in the near-infrared with adaptive optics observations in 2002. While earlier data exists in form of speckle imaging (1995 - 2005), Sgr A* was not detected in the initial analysis. Here, we improved our speckle holography analysis techniques. This has improved the sensitivity of the resulting speckle images by up to a factor of three. Sgr A* is now detectable in the majority of epochs covering 7 years. The brightness of Sgr A* in the speckle data has an average observed K magnitude of 16.0, which corresponds to a dereddened flux density of $3.4$ mJy. Furthermore, the flat power spectral density (PSD) of Sgr A* between $\sim$80 days and 7 years shows its uncorrelation in time beyond the proposed single power-law break of $\sim$245 minutes. We report that the brightness and its variability is consistent over 22 years. This analysis is based on simulations using Witzel et al. (2018) model to characterize infrared variability from 2006 to 2016. Finally, we note that the 2001 periapse of the extended, dusty object G1 had no apparent effect on the near-infrared emission from accretion flow onto Sgr A*. The result is consistent with G1 being a self-gravitating object rather than a disrupting gas cloud.