Continuing Brightening of a Sgr A Complex Molecular Cloud: Revealing More Details about Past Sgr A* Activities

X-ray-bright molecular clouds in the Galactic Center region act as X-ray reflection nebula that can reveal the past activity of the central supermassive black hole Sgr A*. One of the giant molecular clouds in the Sgr A complex, the so-called “the Bridge” gas cloud, is located at ~18 parsecs in projected distance from Sgr A*. Our most recent observation of “the Bridge” gas cloud from 2020 by NuSTAR, combined with archival data in 2012 and 2016, has revealed that this molecular cloud has brightened up in the past eight years. The X-ray flux of the Bridge has indeed doubled in 2020 as compared to 2012. Such brightening of the Bridge may reveal more about Sgr A* activity in the past tens of years and constrain the X-ray reflection nebula models with NuSTAR’s broadband X-ray capacity.