Simultaneous measurement of drifts and noise coefficients of oscillators: Application to the analysis of the time stability of the millisecond pulsars

It is demonstrated that the least square method is unable to separate a linear drift and a low-frequency noise. Moreover, the use of a single variance cannot distinguish a linear frequency drift from a f ² frequency noise if it is calculated in the frequency domain, or a linear frequency drift from a f³ frequency noise if it is calculated in the time domain. Since f³ frequency noise may be encountered in pulsar timing data, this latter solution cannot be used. Hence, the multivariance method using variances calculated in both time and frequency domains seems to be the best solution in this case. Moreover, the great separability of a multivariance system using two types of variances increases the interest of this method