Detection of Seven Sgr A* High-energy X-Ray Flares using 1.3 Ms NuSTAR Observations from 2016 to 2022

Supermassive blackholes exist in almost all the galaxies with a bulge component. Sgr A*, the supermassive blackhole at the center of the Milky Way, exhibits unique flaring activities on a daily basis. During the flares, Sgr A*'s X-ray luminosity increases by a factor of ~10-400. Using new and archival X-ray observations obtained by NuSTAR from 2016 to 2022, totally 1.33 Ms exposure time, we studied Sgr A* X-ray variability and searched for flare events. As a result, we detected a total of seven bright flares, doubled previously detected bright Sgr A* flares as reported in the literature. A notable flare detected in 2018 demonstrates a double-peak feature separated by 15 minutes, suggesting fast recovery of physical conditions such as magnetic field strength. These newly detected flares in the broad X-ray band will allow us to investigate flare spectral dependence on their luminosity, and to constrain the radiation mechanism as well.