  Super-Massive Black Holes reside in galactic nuclei, where they exhibit
episodic bright flares due to accretion events. Taking into account
relativistic effects, namely, the boosting and lensing of X-ray flares, we
further examine the possibility to constraint the mass of the SMBH from the
predicted profiles of the observed light curves. To this end, we have studied
four bright flares from Sagittarius A*, which exhibit an asymmetric shape
consistent with a combination of two intrinsically separate peaks that occur
with a specific time delay with respect to each other. We have thus proposed
(Karssen et al. 2017, Mon. Not. R. Astron. Soc. 472, 4422) that an interplay of
relativistic effects could be responsible for the shape of the observed light
curves and we tested the reliability of the method.
