TY - JOUR
T1 - Corona-heated Accretion-disk Reprocessing
T2 - A Physical Model to Decipher the Melody of AGN UV/Optical Twinkling
AU - Sun, Mouyuan
AU - Xue, Yongquan
AU - Brandt, W. N.
AU - Gu, Wei Min
AU - Trump, Jonathan R.
AU - Cai, Zhenyi
AU - He, Zhicheng
AU - Lin, Da Bin
AU - Liu, Tong
AU - Wang, Junxian
N1 - Funding Information:
2020-03-10 2020-03-18 12:23:51 cgi/release: Article released bin/incoming: New from .zip NSFC 11603022 NSFC 11973002 the 973 Program 2015CB857004 NSFC 11890693 NSFC 11421303 the CAS Frontier Science Key Research Program QYZDJ-SSW-SLH006 NSF AST-1516784 NASA 80NSSC19K0961 NSFC 11925301 NASA STScI HST-GO-15260 NASA STScI HST-GO-15650 NSFC 11873045 NSFC 11822304 yes
PY - 2020/3/10
Y1 - 2020/3/10
N2 - Active galactic nuclei (AGNs) have long been observed to "twinkle" (i.e., their brightness varies with time) on timescales from days to years in the UV/optical bands. Such AGN UV/optical variability is essential for probing the physics of supermassive black holes (SMBHs), the accretion disk, and the broad-line region. Here, we show that the temperature fluctuations of an AGN accretion disk, which is magnetically coupled with the corona, can account for observed high-quality AGN optical light curves. We calculate the temperature fluctuations by considering the gas physics of the accreted matter near the SMBH. We find that the resulting simulated AGN UV/optical light curves share the same statistical properties as the observed ones as long as the dimensionless viscosity parameter , which is widely believed to be controlled by magnetohydrodynamic (MHD) turbulence in the accretion disk, is about 0.01-0.2. Moreover, our model can simultaneously explain the larger-than-expected accretion disk sizes and the dependence of UV/optical variability upon wavelength for NGC 5548. Our model also has the potential to explain some other observational facts of AGN UV/optical variability, including the timescale-dependent bluer-when-brighter color variability and the dependence of UV/optical variability on AGN luminosity and black-hole mass. Our results also demonstrate a promising way to infer the black-hole mass, the accretion rate, and the radiative efficiency, thereby facilitating understanding of the gas physics and MHD turbulence near the SMBH and its cosmic mass growth history by fitting the AGN UV/optical light curves in the era of time-domain astronomy.
AB - Active galactic nuclei (AGNs) have long been observed to "twinkle" (i.e., their brightness varies with time) on timescales from days to years in the UV/optical bands. Such AGN UV/optical variability is essential for probing the physics of supermassive black holes (SMBHs), the accretion disk, and the broad-line region. Here, we show that the temperature fluctuations of an AGN accretion disk, which is magnetically coupled with the corona, can account for observed high-quality AGN optical light curves. We calculate the temperature fluctuations by considering the gas physics of the accreted matter near the SMBH. We find that the resulting simulated AGN UV/optical light curves share the same statistical properties as the observed ones as long as the dimensionless viscosity parameter , which is widely believed to be controlled by magnetohydrodynamic (MHD) turbulence in the accretion disk, is about 0.01-0.2. Moreover, our model can simultaneously explain the larger-than-expected accretion disk sizes and the dependence of UV/optical variability upon wavelength for NGC 5548. Our model also has the potential to explain some other observational facts of AGN UV/optical variability, including the timescale-dependent bluer-when-brighter color variability and the dependence of UV/optical variability on AGN luminosity and black-hole mass. Our results also demonstrate a promising way to infer the black-hole mass, the accretion rate, and the radiative efficiency, thereby facilitating understanding of the gas physics and MHD turbulence near the SMBH and its cosmic mass growth history by fitting the AGN UV/optical light curves in the era of time-domain astronomy.
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U2 - 10.3847/1538-4357/ab789e
DO - 10.3847/1538-4357/ab789e
M3 - Article
AN - SCOPUS:85084088806
VL - 891
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 178
ER -