Optical variability of quasars with 20-yr photometric light curves

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 ∼2...

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Published in:Monthly notices of the Royal Astronomical Society 2022-06, Vol.514 (1), p.164-184
Main Authors: Stone, Zachary, Shen, Yue, Burke, Colin J, Chen, Yu-Ching, Yang, Qian, Liu, Xin, Gruendl, R A, Adamów, M, Andrade-Oliveira, F, Annis, J, Bacon, D, Bertin, E, Bocquet, S, Brooks, D, Burke, D L, Carnero Rosell, A, Carrasco Kind, M, Carretero, J, da Costa, L N, Pereira, M E S, De Vicente, J, Desai, S, Diehl, H T, Doel, P, Ferrero, I, Friedel, D N, Frieman, J, García-Bellido, J, Gaztanaga, E, Gruen, D, Gutierrez, G, Hinton, S R, Hollowood, D L, Honscheid, K, James, D J, Kuehn, K, Kuropatkin, N, Lidman, C, Maia, M A G, Menanteau, F, Miquel, R, Morgan, R, Paz-Chinchón, F, Pieres, A, Plazas Malagón, A A, Rodriguez-Monroy, M, Sanchez, E, Scarpine, V, Serrano, S, Sevilla-Noarbe, I, Smith, M, Suchyta, E, Swanson, M E C, Tarlé, G, To, C
Format: Article
Language:eng ; nor
Subjects:
ASTRONOMY AND ASTROPHYSICS
quasars
Sciences of the Universe
supermassive black holes
surveys
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Summary: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.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stac1259