Discussion and conclusions

Ball & Kirk [2000a] argued that inverse Compton emission from the freely-expanding portion of the wind of PSR B1259-63 should be detectable at energies somewhere between GeV and TeV, depending on the wind parameters. The results presented in Section 3 suggest that even if the wind of the Be star dominates that of the pulsar, terminating it in a shock which wraps around the pulsar, the scattered emission should still be detectable for a wide range of wind parameters. However, the TS has the effect of decreasing the peak integrated -ray flux from the freely-expanding wind, and of decreasing the asymmetry which otherwise produces a characteristic light curve which shows a higher -ray flux before periastron than after.

Even if the Be-star wind dominates to such a degree that the unshocked pulsar wind is not detectable, the models of Kirk, Ball & Skjæraasen [1999] indicate that inverse Compton emission from the shocked pulsar wind should be above the thresholds of current detectors.

The scattered -ray signal from this system is most likely to comprise a combination of emission from the shocked and unshocked regions of the pulsar wind. The reduced asymmetry and periastron to apastron ratio of the emission from the terminated wind may make it harder to deconvolve the two contributions, but only detailed modelling of real data will provide such answers.

The best opportunity for detecting such emission in the near future is afforded by the new CANGAROO II imaging Cherenkov telescope located in Australia [Yoshikoshi et al. 1999]. When the present lack of operational -ray telescopes is relieved by the launch of the GLAST and INTEGRAL observatories, inverse Compton emission from this pulsar system may well be detectable at lower energies in the MeV-GeV range.

The next periastron of PSR B1259-63 occurs in October 2000. CANGAROO II observations of the system will not be possible at times near periastron because at that time the object will be too close to the Sun. In any event, the light curves shown in Figures 5 and 6 are not realistic between about days -25 and +25 because we have not modelled the interaction with the Be-star disk which is important at such epochs. Observations of the PSR B1259-63 system with CANGAROO II are planned for July and December 2000, when our models of the inverse Compton emission from the system should be applicable. If such observations are successful in detecting hard -ray emission from this unique pulsar system they should provide valuable insights into the properties of the pulsar wind. In particular, detection of inverse Compton -ray emission from the system should help to constrain values of the bulk Lorentz factor of the pulsar wind and the fraction of the spin-down luminosity carried by electrons and positrons compared to ions.

© Copyright Astronomical Society of Australia 1997