Evidence for two Lognormal States in Multi-wavelength Flux Variation of FSRQ PKS 1510-089

Abstract

We present a systematic characterization of multi-wavelength emission from blazar PKS 1510-089 using well-sampled data at infrared(IR)-optical, X-ray and $\gamma$-ray energies. The resulting flux distributions, except at X-rays, show two distinct lognormal profiles corresponding to a high and a low flux level. The dispersions exhibit energy dependent behavior except for the LAT $\gamma$-ray and optical B-band. During the low level flux states, it is higher towards the peak of the spectral energy distribution, with $\gamma$-ray being intrinsically more variable followed by IR and then optical, consistent with mainly being a result of varying bulk Lorentz factor. On the other hand, the dispersions during the high state are similar in all bands expect optical B-band, where thermal emission still dominates. The centers of distributions are a factor of $\sim 4$ apart, consistent with anticipation from studies of extragalactic $\gamma$-ray background with the high state showing a relatively harder mean spectral index compared to the low state.

accepted for publication in the ApJL (13 pages, 2 Figures and 3 Tables)