Abstract
Multiwavelength blazar variability is produced by noise-like processes with the power-law form of power spectral density (PSD). We present the results of our detailed investigation of multiwavelength ( γ -ray and optical) light curves covering decades to minutes timescales, of two BL Lac objects namely, PKS 0735+178 and OJ 287. The PSDs are derived using discrete Fourier transform (DFT) method. Our systematic approach reveals that OJ 287 is, on average, more variable than PKS 0735+178 at both optical and γ -ray energies on the corresponding time scales. On timescales shorter than ∼10 days, due to continuous and dense monitoring by the Kepler satellite, a steepening of power spectrum is observed for OJ 287. This indicates the necessity of an intermittent process generating variability on intra-night timescales for OJ 287.
Highlights
Blazars are relatively a rare class of active galactic nuclei (AGN) whose total radiative energy output is dominated by the Doppler-boosted, broad-band and non-thermal processes; synchrotron and inverse-Compton (IC; ∼X-ray–to–γ-ray) occurring in relativistic jets [1]
−β defined as P(νk ) ∝ νk where νk is the temporal frequency and β is the slope), indicate that the variability is generated by correlated noise-like processes on timescales ranging from decades to minutes [8]
The results reported here allowed us to extend the optical power spectral density (PSD) of OJ 287 down to minutes timescales with the usage of the intra-night light curve, which were not covered earlier due to high instrumental noise floor of the Kepler measurements [23]
Summary
Blazars are relatively a rare class of active galactic nuclei (AGN) whose total radiative energy output is dominated by the Doppler-boosted, broad-band and non-thermal processes; synchrotron (radio–to–optical) and inverse-Compton (IC; ∼X-ray–to–γ-ray) occurring in relativistic jets [1]. Besides showing extreme luminosities up to ∼1047−48 ergs s−1 [2], blazars are extremely variable on timescales ranging from decades to hours and even down to minutes with intensity changes of a factor of few, especially prominent at X-ray and γ-ray energies [3,4]. The origin of such dramatic flux changes, in particular their relation to larger amplitude variability, typically 1–2 orders of magnitude, but on longer timescales is still widely debated [5]. We present a comparative study of the synchrotron and the IC variability of two BL
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