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tokens: y -axis, and time is given on the x -axis in days. 2.1. Perturbation in an Accretion Disk One purpose of our model is to simulate the long-term variability in SMBHBs. The variability can be caused by the dynamical parameters of the system, as is shown in Figure 1 , but also by the intrinsic variability of one of the components. As often observed in the light curves of single active galactic nuclei (AGNs), under long-term monitoring, the flux perturbations are present in the form of outbursts (Shapovalova et al. 2010 ; Graham et al. 2017 ), in the form of long-lasting flares as in the case of binary black hole candidates NGC 4151 (see Figure 2 in Shapovalova et al. 2008 ) and E1821+643 (Shapovalova et al. 2017 ), or as remarkably low states or minimum states characterized by an exceptionally weak continuum and line fluxes, also seen in the case of binary black hole candidates NGC 4151 (Shapovalova et al. 2008 ) and NGC 5548 (Bentz et al. 2007 ). The long-term variability of some objects has been successfully modeled by the variety of disk perturbations ranging from the precession of an elliptical disk, or a disk with a spiral arm, to bright spots, highly ionized fast accretion disk outflows, and rotated, sheared, and decayed bright spots (see Jovanović et al. 2010 ; Popović et al. 2012 , and references therein) and cold spots (Kasliwal et al. 2017 ). The perturbations are well localized in the light curve, which possibly reflects the sharp edges of the emission region, and usually resemble a Gaussian-like form. If the angular dimension of the emission region is much smaller than the viewing angle, a distant observer could not detect the anisotropy of its radiation. Based on the above reasons, the perturbations in the light curves have been modeled with Gaussian, exponential, and various other functional forms (e.g., Valtaoja et al. 1999 ; Kudryavtseva et al. 2011 ; Angelakis et al. 2015 ). Kaulakys Alaburda ( 2009 ) and Kelly et al. ( 2011 ) proposed models of light curves based on superpositions of exponentially decaying perturbations occurring at random times and with random amplitudes (the latter is also recognized as Gaussian process regression). Gaussian-like perturbations could arise from the intrinsic quasar variability, for example, the convergence of the Poissonian process once applied to the AGN light curve as reported by Pecháček et al. ( 2008 , 2013 ) can be understood in the general statistical sense as convergence to the Gaussian random process (Fageot et al. 2017 ). Based on previous discussion, there is some evidence that the Gaussian-shaped perturbations are seen in AGNs and even in magnetohydrodynamical simulations, though it is not the only type that can emerge. Usually considered perturbation is in the form of an outburst, which is obtained directly from the magnetohydrodynamic simulation with a hot spot in the disk (Balbus Hawley 1991 ; Abramowicz et al. 1992 ; Poutanen Fabian 1999 ; Życki 2002 ; Armitage Reynolds 2003 ;