Periodic variability of the z = 2.0 quasar QSO B1312+7837

We report here the first results from a 15-yr long variability monitoring of the z=2.0 quasar QSO B1312+7837. It shows luminosity changes with a period P~6.13 yr (P~2.04 yr at rest frame) and an amplitude of ~0.2mag, superimposed on a gradual dimming at a rate of ~0.55mag per 100 yrs. Two false periods associated with power peaks in the data windowing function were discarded. The measured period is confirmed with a bootstrapping Monte-Carlo simulation. A damped random walk model yields a better fit to the data than a sine-function model, but at the cost of employing some high frequency variations which are typically not seen in quasars. We consider the possible mechanisms driving this variability, and conclude that orbital motion of two supermassive black holes - result from a recent galaxy merger - is a possible explanation.