Analysis of time series in space maser signals
Many astrophysical sources that emit narrow radio-frequency spectral lines are believed to be sets of molecular condensation, each of which works as a maser, so that the whole set produces a characteristic spectrum. The forms of these spectra vary with time on various time-scales from months to dozens of minutes. We analysed the ultra-short variations of the separate components of space maser spectra in search for the periodical behaviour. We used a consecutive statistical analysis of the observation data that includes fast Fourier transformations (FFTs), a Lomb-Scargle procedure, and a modified Lomb-Scargle procedure. In at least 8 of the 49 sources we studied, we found that the intensity of one of the components of a space maser spectrum that corresponds to a single condensation changes periodically with a period of dozens of minutes or hours. Three sources had a period of 68 min; in one source the oscillations lasted at least four days.