The nearly periodic fluctuations of blazars in long-term X-ray light curves.

By means of structure function method, we have analyzed 20 blazars observed by the Rossi X-Ray Timing Explorer (RXTE) to search for possible variability period. There are the year-like periodic values in 11 of these blazars. The year-like periodicities in AO 0235+164, Mrk 501, 3C 273 and PKS 1510-089 are also found by the discrete correlation function method, the Jurkevich method and the power spectrum method. AO 0235+164, Mrk 501 and 3C 273 have possible nearly periodic values of about 370 days, 630 days and 370 days, respectively. PKS 1510-089 has two nearly periodic components, about 230 and 330 days. The year-like periodicities could be explained in the framework of a binary black hole system. The turbulence behind a shock may also give rise to the year-like periodicities, dominated by the dominant eddies' turnover times. Also, the year-like periodicities may be from the interplay of a shock with essentially helical structures wrapping around a relativistic jet. [ABSTRACT FROM AUTHOR]