We report the presence of a 106-day cycle in the radio variability of Sgr A* based on an analysis of data observed with the Very Large Array ( VLA ) over the past 20 years .
The pulsed signal is most clearly seen at 1.3 cm with a ratio of cycle frequency to frequency width f / \Delta f = 2.2 \pm 0.3 .
The periodic signal is also clearly observed at 2 cm .
At 3.6 cm the detection of a periodic signal is marginal .
No significant periodicity is detected at both 6 and 20 cm .
Since the sampling function is irregular we performed a number of tests to insure that the observed periodicity is not the result of noise .
Similar results were found for a maximum entropy method and periodogram with CLEAN method .
The probability of false detection for several different noise distributions is less than 5 % based on Monte Carlo tests .
The radio properties of the pulsed component at 1.3 cm are spectral index \alpha \sim 1.0 \pm 0.1 ( for S \propto \nu ^ { \alpha } ) , amplitude \Delta S = 0.42 \pm 0.04 { Jy } and characteristic time scale \Delta t _ { FWHM } \approx 25 \pm 5 days .
The lack of VLBI detection of a secondary component suggests that the variability occurs within Sgr A* on a scale of \sim 5 AU , suggesting an instability of the accretion disk .