TY - JOUR
T1 - Universality in the random walk structure function of luminous quasi-stellar objects
AU - Tang, Ji Jia
AU - Wolf, Christian
AU - Tonry, John
N1 - Publisher Copyright:
© 2023, The Author(s), under exclusive licence to Springer Nature Limited.
PY - 2023/4
Y1 - 2023/4
N2 - Rapidly growing black holes are surrounded by accretion disks that make them the brightest objects in the Universe. Their brightness is known to be variable, but the causes of this are not implied by simple disk models and still debated. Due to the small size of accretion disks and their great distance, there are no resolved images addressing the puzzle. In this work, we study the dependence of their variability on luminosity, wavelength and orbital/thermal timescale. We use over 5,000 of the most luminous such objects with light curves of almost nightly cadence from >5 years of observations by the NASA/ATLAS project, which provides 2 billion magnitude pairs for a structure function analysis. When time is expressed in units of orbital or thermal timescale in thin-disk models, we find a universal structure function, independent of luminosity and wavelength, supporting the model of magneto-rotational instabilities as a main cause. Over a >1 dex range in time, the fractional variability amplitude follows log(A/ A) ≃ 1 / 2 × log(Δ t/ tth). Deviations from the universality may hold clues as to the structure and orientation of disks.
AB - Rapidly growing black holes are surrounded by accretion disks that make them the brightest objects in the Universe. Their brightness is known to be variable, but the causes of this are not implied by simple disk models and still debated. Due to the small size of accretion disks and their great distance, there are no resolved images addressing the puzzle. In this work, we study the dependence of their variability on luminosity, wavelength and orbital/thermal timescale. We use over 5,000 of the most luminous such objects with light curves of almost nightly cadence from >5 years of observations by the NASA/ATLAS project, which provides 2 billion magnitude pairs for a structure function analysis. When time is expressed in units of orbital or thermal timescale in thin-disk models, we find a universal structure function, independent of luminosity and wavelength, supporting the model of magneto-rotational instabilities as a main cause. Over a >1 dex range in time, the fractional variability amplitude follows log(A/ A) ≃ 1 / 2 × log(Δ t/ tth). Deviations from the universality may hold clues as to the structure and orientation of disks.
UR - http://www.scopus.com/inward/record.url?scp=85147311694&partnerID=8YFLogxK
U2 - 10.1038/s41550-022-01885-8
DO - 10.1038/s41550-022-01885-8
M3 - Article
SN - 2397-3366
VL - 7
SP - 473
EP - 480
JO - Nature Astronomy
JF - Nature Astronomy
IS - 4
ER -