code: def powerlaw(f, log10_A=-16, gamma=5):
      
  
      fyr = 1 / 3.16e7
      return (10**log10_A)**2 / 12.0 / np.pi**2 * fyr**(gamma-3) * f**(-gamma)
docs: Power-law PSD.
  
      :param f: Sampling frequencies
      :param log10_A: log10 of red noise Amplitude [GW units]
      :param gamma: Spectral index of red noise process