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

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 ∼80 days and 7 years 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 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.

Search for a Variation of the Fine Structure Constant around the Supermassive Black Hole in Our Galactic Center

“…We infer the radial acceleration experienced by the stars using 25 years of astrometric measurements of the GC. Between 1995 and 2005, speckle imaging data provides astrometric diffraction-limited measurements of the central 5" × 5" of the GC [26,28,49]. Between 2005 and 2018, adaptive optics (AO) imaging provides high-resolution images of the central 10"× 10" of the GC [26,28].…”

A Hidden Friend for the Galactic Center Black Hole, Sgr A*

“…One of the striking observational features that is associated with accretion flow in the center of the galaxy is the variability in radio, near-infrared (NIR), and X-ray radiation (e.g., Zhao et al 2001;Hornstein et al 2002;Ghez et al 2004;Miyazaki et al 2004;Uttley et al 2005;Gillessen et al 2006;Yusef-Zadeh et al 2007, 2011Neilsen et al 2013;Subroweit et al 2017;Witzel et al 2018;Chen et al 2019;Do et al 2019b). The variability can take place on a timescale of minutes to hundreds of minutes, with characteristic coherence timescale of about 243 +82 −57 minutes (Witzel et al 2018).…”

Simulations of M87 and Sgr A* Imaging with the Millimetron Space Observatory on near-Earth orbits

“…It seems obvious and is confirmed both in observations and in numerical simulations, that the flow of innermost accretion and its emissivity are time dependent, and such are also their images around the shadow as well. Near-infrared (NIR) monitoring of Sgr A* reveals variability on a wide range of time scales from 20 s to hours with variations of magnitude up to factor of 10 (Witzel et al 2018;Chen et al 2019). Besides such regular oscillations of disc emissivity, strong sporadic flares can also happen in the innermost region, such as, e.g., the "non-thermal bomb" in May 2019 detected in NIR at the Keck Telescope (Do et al 2019) and occurred apparently within ∼ 10r g of the innermost accretion flow (Gutiérrez et al 2020).…”