The 1997 periastron passage of the binary pulsar PSR B1259-63

We report here on multifrequency radio observations of the pulsed emission from PSR B1259-63 around the time of the closest approach (periastron) to its B2e companion star. There was a general increase in the dispersion measure (DM) and scatter-broadening of the pulsar, and a decrease in the flux density towards periastron although fluctuation in these parameters were seen on time-scales as short as minutes. The pulsed emission disappeared 16d prior to periastron and remained undetectable until 16d after periastron. The observations are used to determine the parameters of the wind from the Be star. We show that a simple model, in which the wind density varies with radius as r-2, provides a good fit to the data. The wind is highly turbulent with an outer scale of <=1010cm and an inner scale perhaps as small as 104cm, a mean density of ~106cm-3 and a velocity of ~2000kms-1 at a distance of ~50 stellar radii. We find a correlation between DM variations and the pulse scattering times, suggesting that the same electrons are responsible for both effects.