The gamma-ray source LSI +61°303

An analysis of RXTE/ASM observations of the unusual binary system LSI +61°303 is presented. The X-ray light curve gives a binary period of $26.42 \pm 0.05$ days, and an eccentricity of $0.30 \pm 0.04$ (1σ). The eccentricity is determined by fitting an inverse Compton model to the X-ray light curve. These are the best determinations to date, as the optical period and eccentricity have larger uncertainties and published values of the radio period are variable. The radio outburst peak is not phase locked to the binary period, so the radio period is not the same as the binary period