We present the timing analysis results for our observations of the x-ray dip source X1916-053 conducted with RXTE between February and October of 1996 .
Our goal was to finally measure the binary period - as either the x-ray dip period or \sim 1 % longer optical modulation period , thereby establishing if the binary has a precessing disk ( SU UMa model ) or a third star ( triple model ) .
Combined with historical data ( 1979-96 ) , the x-ray dip period is measured to be 3000.6508 \pm 0.0009 sec with a 2 \sigma upper limit | \dot { P } | \leq 2.06 \times 10 ^ { -11 } .
From our quasi-simultaneous optical observations ( May 14-23 , 1996 ) and historical data ( 1987-96 ) , we measure the optical modulation period to be 3027.5510 \pm 0.0052 sec with a 2 \sigma upper limit | \dot { P } | \leq 2.28 \times 10 ^ { -10 } .
The two periods are therefore each stable ( over all recorded data ) and require a 3.9087 \pm 0.0008 d beat period .
This beat period , and several of its harmonics is also observed as variations in the dip shape .
Phase modulation of x-ray dips , observed in a 10 consecutive day observation , is highly correlated with the \sim 3.9d dip shape modulation .
The 1987-1996 optical observations show that the optical phase fluctuations are a factor of 3 larger than those in the x-ray .
We discuss SU UMa vs. triple models to describe the X1916-053 light curve behavior and conclude that the x-ray dip period , with smaller phase jitter , is probably the binary period so that the required precession is most likely similar to that observed in SU UMa and x-ray nova systems .
However the “ precession ” period stability and especially the fact that the times of x-ray bursts may partially cluster to occur just after x-ray dips , continue to suggest that this system may be a hierarchical triple .