text: In equations 3 and 4, τ is called the “relaxation 
  time” of the process S(t) and is identiﬁed by the 
  break in PX (f ). The power spectrum appears ﬂat 
  for timescales longer than this and falls oﬀ as 1/f 2 for 
  timescales shorter than the characteristic timescale of 
  the process.  **4. CONNECTION WITH GAMMA-RAYS**
  
  Taking the logarithm of the blazar light curve (in 
  Jy) to be S(t), we adopt τ (in days) as the character- 
  istic timescale of variability, after which the physical 
  process “forgets” about what has happened at time 
  lags of greater than τ . The two other relevant pa- 
  rameters, σ and µ = b/a, are the overall amplitude 
  of variability and the logarithm of mean value of the 
  light curve, respectively. 
  
  In the routine, we construct an autoregressive 
  model for the light curves for a minimum of 100,000 
  iterations and calculate the value of τ from the break 
  in the power spectrum in each instance. Due to the 
  limited number of observations in the 850µm band, 
  we performed this autoregressive analysis only for the 
  1mm light curves, which typically have more than 10 
  points per light curve. 