02921nas a2200457   4500000000100000000000100001008004100002100001900043700002100062700002300083700001700106700002200123700001800145700002300163700001700186700001800203700001500221700002300236700001900259700001600278700002200294700001600316700002600332700002300358700001700381700002100398700001600419700002100435700001400456700001600470700002300486700001900509700001700528700002000545700002400565700004600589245010800635300000900743490000800752520170300760       2022                            d1 aBoris Georgiev1 aDominic W. Pesce1 aAvery E. Broderick1 aVedant Dhruv1 aCharles F. Gammie1 aChi-Kwan Chan1 aKoushik Chatterjee1 aRazieh Emami1 aYosuke Mizuno1 aRoman Gold1 aChristian M. Fromm1 aAngelo Ricarte1 aDoosoo Yoon1 aAbhishek V. Joshi1 aBen Prather1 aAlejandro Cruz-Osorio1 aMichael D. Johnson1 aOliver Porth1 aHéctor Olivares1 aZiri Younsi1 aLuciano Rezzolla1 aJesse Vos1 aRichard Qiu1 aAntonios Nathanail1 aRamesh Narayan1 aAndrew Chael1 aRichard Anantua1 aMonika Moscibrodzka1 aThe Event Horizon Telescope Collaboration00aA Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows   a1-320 v9303 a<p>	We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT.</p>