Light curve of 3C 273

The historical light curve of 3C 273 is analyzed using the technique of autoregressive (AR) decomposition. The observed optical fluctuations are regarded as the output of a linear system whose input is shot noise. The AR representation of this process is computed in a way consistent with the principle of maximum entropy and makes use of the Akiake final prediction error criterion for choosing the order of the process. Inversion of the AR parameters yields the minimum delay impulse response of the linear system. The technique further allows the computation of the optimally smoothed maximum entropy power spectrum. Numerical examples based on the shot-noise model of 3C 273 discussed by Terrell and Olsen are presented. The application to the observed light curve of 3C 273 indicates that no low-frequency cyclic component is present and the characteristic optical pulse responsible for the observed variability qualitatively resembles the light curve of a supernova. However, the time scale is one order of magnitude longer and, at the cosmological distance of 3C 273, the total energy release in the pulse is some three orders of magnitude greater than for conventional supernovae