Tools for period searching in AGN in the era of "Big Data"

Tools for period searching in AGN in the era of "Big Data"

Saikruba Krishnan, Alex Markowitz, Aleksander Schwarzenberg-Czerny

Active Galactic Nuclei (AGN) persistently emit across the electromagnetic spectrum and are dominated by stochastic, aperiodic emission that is variable on timescales from hours to decades. Because pure stochastic red noise signals spuriously mimic few-cycle periods, the presence of the stochastic variability impedes our ability to robustly confirm if any periodic signals are present in AGN. In addition, we have already entered the era of “Big Data,” with current and near-future large-area monitoring programmes such as LSST facilitating data trawls for periodicities; developing the proper know-how for period searching is thus essential. Hence in our project we try to account for the presence of red noise using various methods — Auto-correlation Function (ACF), Phase dispersion minimization (PDM), wavelet analysis and Bayesian analysis — and test if each method can robustly distinguish between pure red-noise processes and mixtures of a strictly- or quasi-periodic signal (QPO) with red noise, while pursuing the following questions: When the variability process is pure red noise (no QPO present), what is the false-alarm probability and how does it depend on broadband continuum power spectral density (PSD) shape? When there is intrinsically a mixture of red noise and a QPO, is there a range in detection sensitivity between the various methods as a function of broadband spectral slopes and different strengths of QPO against the red noise? Here we present some preliminary results from analysis in progress using the ACF and the PDM. We compare our results to models of binary supermassive black hole (SMBH) systems to constrain the regions of parameter space where detection of periodicities due to binary orbital motion against red noise from the accretion disk is feasible with typical ground-based monitoring programs.

Proceedings of the Polish Astronomical Society, vol. 10, 237-242 (2020)

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