Search for optical microvariability in a large sample of Seyfert I galaxies

We present results of an optical (I band) monitoring of a sample of 22 Seyf ert I galaxies. We aimed to detect mi crovariability with time resolution f rom similar or equal to 6 minutes down to 30 seconds for the most luminous one. It is the largest survey ever done in the search of rapid optical vari ations in Seyfert galaxies. We used differential photometry and a new metho d of analysis between galaxy and comparison stars light curves in order to minimize the influence of the intrinsic variabilities of the latter. We thu s obtain precision on standard deviation measurements less than 1% and gene rally of the order of 0.5%. We obtain no clear detection of microvariabilit y in any of these objects. In the hypothesis where optical microvariability could be due to synchrotron emission of a non thermal electrons population , we discuss the physical constraints imposed by these results.