Timing analysis of the brightest X-ray flare of Sagittarius A* detected by XMM-Newton in 2019

XMM-Newton has been monitoring Sgr A*, the supermassive black hole located at the dynamical centre of the Milky Way for more than two decades. A total of 91 observations were conducted from 1999 to 2023. In this paper we focus on a time-binned analysis of 2019 observations with a time coverage of ≈ 460 ks to investigate the flaring activities of Sgr A*. We proceeded background-subtracted light curves of the 2019 datasets for various on- and off-extraction regions to analyse the signal-to-noise ratio of the detected flares of Sgr A* and enhance the statistical significance of its variability in the X-ray band. Our results reveal that Sgr A* underwent six very bright flaring events during the 2019 XMM-Newton observations, from March to the end of September. We identified the five brightest flares of Sgr A*, observed over more than two decades (1999-2023), with two of these events occurring in 2019. Remarkably, Sgr A* exhibited its brightest flaring event reported so far on August 31, 2019 with a peak brightness and duration exceeding the previous four brightest flares by more than a factor of 2. This exceptionally bright flare, with a duration of 6.6 ks, featured an asymmetric energy-independent double-peak morphology. Spectral analysis of this double-peaked flare suggests spectral evolution during the event and highlights substructures on timescales as short as 100s. We discuss the implications of the observed flaring activity for synchrotron and hotspot emission models.