TTVs are derived from Q1-Q15 Kepler data. x-axes: “Observed Tc” (Mid-Transit Time): EXOFAST’s best-fits from Kepler light flux vs. time data. y-axes: “(O – C)”: difference between Observed Tc and the Calculated Tc from the graphically obtained linear ephemeris. The plots are pictured in the order of orbital periods.
The TTV plot strongly suggests the presence of at least one more non-transiting exoplanet in this star system. Note the particularly close agreement between the P_ttv (from the best-fit sinusoidal curve) and the major Lomb-Scargle periodogram peak: 958.90 vs. 972.76 days.