%0 Journal Article %A Edelson, R. %A Mushotzky, R. %A Vaughan, Simon Allan %A Scargle, J. %A Gandhi, P. %A Malkan, M. %A Baumgartner, W. %D 2016 %T Kepler observations of rapid optical variability in the BL Lac object W2R1926+42 %U https://figshare.le.ac.uk/articles/journal_contribution/Kepler_observations_of_rapid_optical_variability_in_the_BL_Lac_object_W2R1926_42/10171706 %2 https://figshare.le.ac.uk/ndownloader/files/18331319 %K BL Lacertae objects: general %K BL Lacertae objects: individual (W2R1926+42) %K galaxies: active %X We present the first Kepler monitoring of a strongly variable BL Lac, W2R1926+42. The light curve covers 181 days with ~0.2% errors, 30 minute sampling and >90% duty cycle, showing numerous delta I/I > 25% flares over timescales as short as a day. The flux distribution is highly skewed and non-Gaussian. The variability shows a strong rms-flux correlation with the clearest evidence to date for non-linearity in this relation. We introduce a method to measure periodograms from the discrete autocorrelation function, an approach that may be well-suited to a wide range of Kepler data. The periodogram is not consistent with a simple power-law, but shows a flattening at frequencies below 7x10-5 Hz. Simple models of the power spectrum, such as a broken power law, do not produce acceptable fits, indicating that the Kepler blazar light curve requires more sophisticated mathematical and physical descriptions than currently in use. %I University of Leicester