Periodic oscillation in the long-term radio light curves of Quasar 1156+295

Based on the light curves at 4.8, 8.0 and 14.5 GHz of Quasar 1156+295 from the University of Michigan Radio Astronomy Observatory, we analyze the variability property of total flux at the three radio bands during the time range from 1980 to 2012. With the structure function (SF) analysis we find a similar evolution trend with the characteristic variability timescale of 1.15±0.05 year for all the three radio bands, and a possible quasi-periodic variability period of ～2.3±0.1 year. The Lomb-Scargle periodogram (LSP) analysis implies the existence of multiple periods in the radio light curves, one of them with a period similar to the one found using the SF at around 2.3 year. The structure function analysis of pre- and post-1997 suggests that the characteristic timescales become longer since 1997, confirmed by the result of Lomb-Scargle periodogram and auto-correlation function. In addition, the cross correlation analysis confirms that there is a strong correlation of flux variations at the three radio frequencies with the 14.5 GHz variation leading the other two bands by about 60–120 days.