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Optical variability of quasars with 20-yr photometric light curves

2022; Oxford University Press; Volume: 514; Issue: 1 Linguagem: Inglês

10.1093/mnras/stac1259

1365-2966

Zachary Stone, Yue Shen, Colin J. Burke, Yu-Ching Chen, Qian Yang, Xin Liu, R. A. Gruendl, M. Adamów, F. Andrade-Oliveira, J. Annis, David 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. Gaztañaga, D. Gruen, G. Gutiérrez, 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, M. Rodríguez-Monroy, E. Sánchez, V. Scarpine, S. Serrano, I. Sevilla-Noarbe, M. Smith, E. Suchyta, M. E. C. Swanson, G. Tarlé, C. To,

Gamma-ray bursts and supernovae

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.