Stellar wind and stellar disc models of dispersion and rotation measure
variations in the PSR B1259-63/SS 2883 binary system
A. Melatos, S. Johnston and D. B. Melrose, RCfTA
Abstract.
Two models of the PSR B1259-63/SS 2882 binary system are evaluated to
determine whether they account for the orbital variations in dispersion
measure (DM) and rotation measure (RM) observed during the 1994 periastron
passage of PSR B1259-63. In the first model, the DM and RM variations are
produced by an ionized, radiatively driven, coronal wind from SS 2883.
The electron density, ne, and magnetic field, B, vary as power laws with
distance r from SS 2882, and the wind terminates where it collides with
the relavtivistic, electron-positron wind from PSR B1259-63. It is shown
that this model - popular in the literature - cannot reproduce the
observed pre-periastron rise in DM unless one has ne proportional to r^-5,
with ne~10^14 cm^-3 at the stellar surface, contrary to the predictions
of dynamical wind theories. In the second model, the DM and RM variations
are due to a cool, dense, circumstellar disc with an exponential density
profile in the radial and vertical directions. Good agreement with the
observations is achieved for a disc inclined ~10 degress to the orbital
plane with ne~10^8 cm^-3 and B~10 kG at the stellar surface, and radial
scale size rd~12 r*. The data do not discriminate between a thin disc
(scaleheight hd<