Consistency of the Infrared Variability of SGR A* over 22 yr

Chen, Zhuo; Gallego-Cano, E.; Do, T.; Witzel, G.; Ghez, A. M.; Schödel, R.; Sitarski, B. N.; Becklin, E. E.; Lu, J.; Morris, M. R.; Dehghanfar, A.; Gautam, A. K.; Hees, A.; Hosek, M. W., Jr; Jia, S.; Mangian, A. C.; Matthews, K.

September, 2019
ABSTRACT: 

We report new infrared (IR) 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 10 times longer than earlier published studies. Sgr A* was initially detected in the near-infrared (NIR) 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 yr. 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 of Sgr A* between ∼80 days and 7 yr shows its uncorrelation in time beyond the proposed single power-law break of ∼245 minutes. We report that the brightness and its variability is consistent over 22 yr. This analysis is based on simulations using the Witzel et al. model to characterize IR variability from 2006 to 2016. Finally, we note that the 2001 periapse of the extended, dusty object G1 had no apparent effect on the NIR emission from accretion flow onto Sgr A*. The result is consistent with G1 being a self-gravitating object rather than a disrupting gas cloud.