  The supermassive black hole Sagittarius A* (Sgr A*) is located at the
dynamical center of the Milky Way. In a recent study of the X-ray flaring
activity from Sgr A* using Chandra, XMM-Newton and Swift data from 1999 to
2015, it has been argued that the bright flaring rate has increased from 2014
Aug. 31 while the faint flaring rate decreased from around 2013 Aug. We tested
the persistence of these changes in the flaring rates with new X-ray data of
Sgr A* obtained in 2016-2018 (total exposure of 1.4Ms). We detected 9 flares in
the Chandra data and 5 flares in the Swift data that we added to the set of 107
previously detected flares. We computed the intrinsic distribution of flare
fluxes and durations corrected for the sensitivity bias using a new method that
allowed us to take the error on the flare fluxes and durations into account.
From this intrinsic distribution, we determined the average flare detection
efficiency for each Chandra, XMM-Newton, and Swift observation. After
correcting each observational exposure for this efficiency, we applied the
Bayesian blocks algorithm on the concatenated flare arrival times. As in the
above-mentioned study, we also searched for a flux and fluence threshold that
might lead to a change in flaring rate. We improved the previous method by
computing the average flare detection efficiencies for each flux and fluence
range. The Bayesian block algorithm did not detect any significant change in
flaring rate of the 121 flares. However, we detected an increase by a factor of
about three in the flaring rate of the most luminous and most energetic flares
that have occurred since 2014 Aug. 30. The X-ray activity of Sgr A* has
increased for more than four years. Additional studies about the overall
near-infrared and radio behavior of Sgr A* are required to draw strong results
on the multiwavelength activity of the black hole.
