A re-analysis of Gliese 667C HARPS precision radial velocity data was carried out with a Bayesian multi-planet Kepler periodogram ( from 0 to 7 planets ) based on a fusion Markov chain Monte Carlo algorithm .
The most probable number of signals detected is 6 with a Bayesian false alarm probability of 0.012 .
The residuals are shown to be consistent with white noise .
The 6 signals detected include two previously reported with periods of 7.198 ( b ) and 28.14 ( c ) days , plus additional periods of 30.82 ( d ) , 38.82 ( e ) , 53.22 , and 91.3 ( f ) days .
The 53 day signal is probably the second harmonic of the stellar rotation period and is likely the result of surface activity .
The existence of the additonal Keplerian signals suggest the possibilty of further planets , two of which ( d and e ) could join Gl 667Cc in the central region of the habitable zone .
N-body simulations are required to determine which of these signals are consistent with a stable planetary system . M \sin i values corresponding to signals b , c , d , e , and f are \sim 5.4 , 4.8 , 3.1 , 2.4 , and 5.4 M _ { \earth } , respectively .