Optical variability of quasars with 20-yr photometric light curves

• DOI: 10.1093/mnras/stac1259
• Publication Date: 2022-05-05T11:15:56Z
• Authors: Zachary Stone; Yue Shen; Colin J Burke; Yu-Ching Chen; Qian Yang; Xin Liu; R A Gruendl; M Adamów; F Andrade-Oliveira; J Annis; D Bacon; E Bertin; S Bocquet; D Brooks; D L Burke; A Carnero Rosell; M Carrasco Kind; J Carretero; L N da Costa; M E S Pereira; J De Vicente; S Desai; H T Diehl; P Doel; I Ferrero; D N Friedel; J Frieman; J García-Bellido; E Gaztanaga; D Gruen; G Gutierrez; S R Hinton; D L Hollowood; K Honscheid; D J James; K Kuehn; N Kuropatkin; C Lidman; M A G Maia; F Menanteau; R Miquel; R Morgan; F Paz-Chinchón; A Pieres; A A Plazas Malagón; M Rodriguez-Monroy; E Sanchez; V Scarpine; S Serrano; I Sevilla-Noarbe; M Smith; E Suchyta; M E C Swanson; G Tarlé; C To
• Keywords: astronomi: 438; astro-ph.GA; Quasars: Supermassive Black Holes; quasars; quasars: supermassive black holes; supermassive black holes; Quasars: supermassive black holes; Física; FOS: Physical sciences; Surveys; Astrophysics - Astrophysics of Galaxies; 520; [SDU] Sciences of the Universe [physics]; Quasars: general; surveys; quasars: general; Astrophysics of Galaxies (astro-ph.GA); Quasars: General; VDP::Astrofysikk

ABSTRACT We study the optical gri photometric variability of a sample of 190 quasars within the SDSS Stripe 82 region that have long-term photometric coverage during ∼1998−2020 with SDSS, PanSTARRS-1, the Dark Energy Survey, and dedicated follow-up monitoring with Blanco 4m/DECam. With on average ∼200 nightly epochs per quasar per filter band, we improve the parameter constraints from a Damped Random Walk (DRW) model fit to the light curves over previous studies with 10–15 yr baselines and ≲ 100 epochs. We find that the average damping time-scale τDRW continues to rise with increased baseline, reaching a median value of ∼750 d (g band) in the rest frame of these quasars using the 20-yr light curves. Some quasars may have gradual, long-term trends in their light curves, suggesting that either the DRW fit requires very long baselines to converge, or that the underlying variability is more complex than a single DRW process for these quasars. Using a subset of quasars with better-constrained τDRW (less than 20 per cent of the baseline), we confirm a weak wavelength dependence of τDRW∝λ0.51 ± 0.20. We further quantify optical variability of these quasars over days to decades time-scales using structure function (SF) and power spectrum density (PSD) analyses. The SF and PSD measurements qualitatively confirm the measured (hundreds of days) damping time-scales from the DRW fits. However, the ensemble PSD is steeper than that of a DRW on time-scales less than ∼ a month for these luminous quasars, and this second break point correlates with the longer DRW damping time-scale.