Statistical analysis of variability properties of the Kepler blazar W2R 1926+42

Abstract

We analysed Kepler light curves of the blazar W2R 1926+42 that provided nearly continuous coverage from quarter 11 to quarter 17 (589 d between 2011 and 2013) and examined some of their flux variability properties. We investigate the possibility that the light curve is dominated by a large number of individual flares and adopt exponential rise and decay models to investigate the symmetry properties of flares. We found that those variations of W2R 1926+42 are predominantly asymmetric with weak tendencies towards positive asymmetry (rapid rise and slow decay). The durations (D) and the amplitudes (F0) of flares can be fit with lognormal distributions. The energy (E) of each flare is also estimated for the first time. There are positive correlations between logD and logE with a slope of 1.36, and between logF0 and logE with a slope of 1.12. Lomb-Scargle periodograms are used to estimate the power spectral density shape. It is well described by a power law with an index ranging between -1.1 and -1.5. The sizes of the emission regions, R, are estimated to be in the range of 1.1 × 1015-6.6 × 1016cm. The flare asymmetry is difficult to explain by a light travel time effect but may be caused by differences between the time-scales for acceleration and dissipation of high-energy particles in the relativistic jet. A jet-in-jet model could also produce the observed lognormal distributions.