A report is made on the luminosity and pulse-period evolution of the Be binary X-ray pulsar , GX 304 - 1 , during a series of outbursts from 2009 to 2013 observed by MAXI/GSC , RXTE/PCA , and Fermi/GBM .
In total , twelve outbursts repeated by \sim 132.2 days \textcolor blackwere observed , which is consistent with the X-ray periodicity of this object observed in the 1970s .
These 12 outbursts , together with those in the 1970s , were found to all recur with a well defined period of 132.189 \pm 0.02 d , which can be identified with the orbital period .
The pulse period at \sim 275 s , obtained from the RXTE/PCA and Fermi/GBM data , apparently exhibited a periodic modulation synchronized with the outburst period , suggesting the pulsar orbital motion , which is superposed on a secular spin-up trend throughout the entire active phase .
The observed pulse-period changes were successfully represented by a model composed of the binary orbital modulation and pulsar spin up caused by mass accretion through an accretion disk .
The orbital elements obtained from the best-fit model , including the projected orbital semi-major axis a _ { x } \sin i \simeq 500 - 600 light-s and an eccentricity e \simeq 0.5 , are typical of Be binary X-ray pulsars .