The long-term optical behavior of BL Lac object S5 0716+714

BL Lac object S5 0716+714 is a well-studied object. In this paper, the available optical ( BVRI ) data of this source are compiled, and the B-, V-, R- and I -band light curves are constructed. Each of them is analyzed by means of the discrete correlation function (DCF) method, the structure function (SF) method and the z -transformed discrete correlation function (ZDCF) method. The results imply that there is a possible periodic variation of 1211 days in each passband light curve. The source varies violently and complicatedly, and exhibits a brightening trend in the light curves.