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&RXQWV 0HDQ 2SWLFDO X V J V U V L V ] V 7LPH V VLQFH VWDUW RI VHFWLRQ )OX[ [ FRXQWV V ; UD\V í NH9 >,QVHW@ 7LPH V í í í í í 'LVFUHWH &RUUHODWLRQ )XQFWLRQ 2SWLFDO /DJ V '&) 2SWLFDO YV ;íUD\V Figure 18: The left panel shows the optical (top) and X-ray (bottom) lightcurves, with intense flaring seen in every band, with optical activity stronger at longer, red wavelengths. The inset shows a zoom-in of a single second ( ∼ 300 frames), where an optical flare follows one in X-rays by ∼ 170ms. The right panel shows the correlation function between the optical bands and X-rays - here, a broad anti-correlation at ∼ second timescales, as well as the optical delay of ∼ 170ms can be seen - this latter feature is apparently common in black hole binaries, and could relate to a jet. ability, Gaussian measurement errors and power spectrum index β (i.e., P ( f ) ∝ f − β ), and provided guidelines for reliable use of skewness and Anderson-Darling (AD) tests. They provided empirical fits to the standard deviations of the skewness and tabulated critical values for the AD test for β = 0.5 and 1.0, which differ from the values given in literature for white noise. The skewness standard deviation and critical values can be used to determine significance by which the tests reject that the distribution is normal. More importantly, they have addressed a conceptually paradoxical issue regarding non-Gaussian flux distributions. While Gaussian distributions remain Gaussian on addi- tion (binning), this in general is not true for other distributions such as a log-normal one. Thus, it is not clear why several astrophysical systems display log-normal distributions when the lightcurves they are estimated from, are always binned to some time-bin? They resolve this issue by showing that if the power spectra of the lightcurves can be described by a power law with index β 0 . 5, then the nature of the distribution is invariant to binning. Thus, for a system to be scale free in time and have a log-normal flux distribution its power spectra must be steeper than 0.5. This insight may have important consequences for the model development and understanding of systems with log-normal distributions. Study of long-term flux and photon index distributions of blazars using RXTE observations Blazars are an extreme class of active galactic nuclei (AGN) with powerful relativistic jets of plasma pointing close to the line of sight of the observer. Rukaiya Khatoon, Zahir Shah , Ranjeev Misra and Rupjyoti Gogoi carried a detailed study of flux and index distributions of three blazars [one flat-spectrum radio quasar (FSRQ), and two BL Lacertae objects (BL Lacs)] by using 16 years of Rossi X-ray Timing Explorer (RXTE) archival data. The blazars were selected such that their flux and index distributions have sufficient number of data points ( ≥ 90) with relatively less uncertainty ( σ 2 err /σ 2 < 0 . 2). Using the AD test and histogram fitting, they showed that flux distribution of FSRQ 3C 273 is lognormal, while its photon index distribution is Gaussian. They interpreted the result interms of linear Gaussian perturbation in the particle acceleration time-scale, which