Study of long-term flux and photon Index distributions of blazars using RXTE observations

Abstract

We present a detailed study of flux and index distributions of three blazars (one FSRQ and two BL Lacs) by using 16 years of Rossi X-ray Timing Explorer archival data. The three blazars were chosen such that their flux and index distributions have sufficient number of data points ($\geq$90) with relatively less uncertainty ($\bar{σ_{err}^{2}}/σ^{2}$<0.2) in light curves. Anderson-Darling (AD) test and histogram fitting shows that flux distribution of FSRQ 3C273 is log-normal, while its photon index distribution is Gaussian. This result is consistent with linear Gaussian perturbation in the particle acceleration time-scale, which produces log-normal distribution in flux. However, for two BL Lacs viz. Mkn501 and Mkn421, AD test shows that their flux distributions are neither Gaussian nor log-normal, and their index distributions are non-normal. The histogram fitting of Mkn501 and Mkn421, suggests that their flux distributions are more likely to be a bi-modal, and their index distributions are double Gaussian. Since, Sinha et al. (2018) had shown that Gaussian distribution of index produces a log-normal distribution in flux, double Gaussian distribution of index in Mkn501 and Mkn421 indicates that their flux distributions are probably double log-normal. Observation of double log-normal flux distribution with double Gaussian distribution in index reaffirms two flux states hypothesis. Further, the difference observed in the flux distribution of FSRQ (3C273) and BL Lacs (Mkn501 and Mkn421) at X-rays, suggest that the low energy emitting electrons have a single log-normal flux distribution while the high energy ones have a double log-normal flux distribution.