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Y. Chou, P.F. Bloser, J.E. Grindlay (CFA)
We present the timing analysis results for the X-ray dipping source X1916-053 observed by RXTE between February and October of 1996. The X-ray dip period is measured to be 3000.6508 ± 0.0021 sec. New optical observations were made from 1996 May 14 to 23. Combined with the 1987 to 1992 optical observations, the optical dip period is measured to be 3027.5510 ± 0.0056 sec. The two periods are significantly different and suggest a ~3.9d beat period. The beat between the X-ray period and several harmonics of ~3.9d can be observed in data from observations performed on 10 consecutive days in May 1996. A light curve-folding analysis shows that the ~3.9d modulation comes from variations in the dip shape. The dip phase analysis shows that the X-ray dip period is stable for the past ~ 17 years with an insignificant period derivative of (3.25 ± 5.43) x 10-8 yr-1, and the dip center phases can be described by a simple ephemeris. The phase jitter phenomenon, observed in the 10 consecutive observations, is highly correlated with the ~3.9d dip shape modulation. The 1987-1996 optical observations show that the optical phase fluctuation is a factor of 3 larger than that in the X-ray. The optical period is stable over ~ 9 years with a period derivative (4.54 ± 6.54) x 10-7 yr-1. We also discuss a possible orbital model to describe the X1916-053 light curve behavior.