Timing residuals against the refined linear ephemeris. Data points are coded as in Fig. 2, and the data from Sokov et al. (2018) are skipped for clarity. The green and red lines show the periodic and quadratic-trend scenarios, respectively. Each bunch consists of 100 lines randomly picked from the Markov chains. Both scenarios remain statistically undistinguished in the time covered by current observations. The models are extrapolated to the next ten years to illustrate the broad spectrum of possible solutions.