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Quasars emission is highly variable, and this variability gives us clues tounderstand the accretion process onto supermassive black holes. We can expectvariability properties to correlate with the main physical properties of theaccreting black hole, i.e., its mass and accretion rate. It has beenestablished that the relative amplitude of variability anti-correlates with theaccretion rate.The dependence of the variance on black hole mass has remainedelusive, and contradicting results, including positive, negative, or nocorrelation, have been reported. In this work, we show that the key to thesecontradictions lies in the timescales of variability studied (e.g., the lengthof the light curves available). By isolating the variance on differenttimescales as well as mass and accretion rate bins we show that there is indeeda negative correlation between black hole mass and variance and that thisanti-correlation is stronger for shorter timescale fluctuations. The behaviorcan be explained in terms of a universal variability power spectrum for allquasars, resembling a broken power law where the variance is constant at lowtemporal frequencies and then drops continuously for frequencies higher than acharacteristic frequency $f_b$, where $f_b$ correlates with the black holemass. Furthermore, to explain all the variance results presented here, not onlythe normalization of this power spectrum must anti-correlate with the accretionrate, but also the shape of the power spectra at short timescales must dependon this parameter as well.

Optical variability in Quasars: Scaling with black hole mass and Eddington ratio depend on the observed timescales