O–C diagrams of the two pairs A and B. The dots stand for the primary, while the open circles for the secondary minima, the bigger the symbol, the higher the weight. The red dash-dotted lines indicate the LTTE fit, while the black and blue curves represent the final fit (LTTE plus the apsidal motion). This solution is taken from our original study in 2013; the grey area indicates where observations are missing exactly in between the two periastron passages.