Hydrodynamic Interaction between the Be Star and the Pulsar in the TeV Binary PSR B1259$-$63/LS 2883

Abstract

We have been studying the interaction between the Be star and the pulsar in the TeV binary PSR B1259$-$63/LS 2883, using 3-D SPH simulations of the tidal and wind interactions in this Be–pulsar system. We first ran a simulation without pulsar wind nor Be wind, while taking into account only the gravitational effect of the pulsar on the Be disk. In this simulation, the gas particles are ejected at a constant rate from the equatorial surface of the Be star, which is tilted in a direction consistent with multi-waveband observations. We ran the simulation until the Be disk was fully developed and started to repeat a regular tidal interaction with the pulsar. Then, we turned on the pulsar wind and the Be wind. We ran two simulations with different wind mass-loss rates for the Be star, one for a B2 V type and the other for a significantly earlier spectral type. Although the global shape of the interaction surface between the pulsar wind and the Be wind agrees with the analytical solution, the effect of the pulsar wind on the Be disk is profound. The pulsar wind strips off an outer part of the Be disk, truncating the disk at a radius significantly smaller than the pulsar orbit. Our results, therefore, rule out the idea that the pulsar passes through the Be disk around periastron, which has been assumed in previous studies. It also turns out that the location of the contact discontinuity can be significantly different between phases when the pulsar wind directly hits the Be disk and those when the pulsar wind collides with the Be wind. It is thus important to adequately take into account the circumstellar environment of the Be star, in order to construct a satisfactory model for this prototypical TeV binary.

Periodic morphological changes in the radio structure of the gamma-ray binary LS 5039

“…A simple and shockless microquasar scenario is disfavoured by previous VLBI radio observations of LS 5039 (Ribó et al 2008). Also, no signs of an accretion disc have been detected so far (although see Okazaki et al 2008, for alternative explanations). Sarty et al (2011) used the stability of the optical photometry of LS 5039 to constrain the orbit inclination to be below 60…”

Multi-wavelength observations of the binary system PSR B1259−63/LS 2883 around the 2014 periastron passage

“…For LS 2883, the Be disk should be highly truncated near periastron, both due to the gravitational influence of the pulsar (which is observed in other Be binaries using long baseline optical interferometry; Gies et al 2007) and due to disruption by the pulsar wind ram pressure (predicted by simulations of Okazaki et al 2011;Takata et al 2012). The truncation distance expands rapidly after periastron passage.…”

“…In addition, the Brγ line is asymmetric (as the HeI 6678 line), with the blue wing slightly wider in March than in January, which is reminiscent of the asymetric double peaked HeI 6678 line. This asymmetry may indicate either the presence of a spiral density wave in the disk as suggested by the observations of HeI 6678 line, or even a truncation of the disk size between the compact object and the companion star (such as described in Okazaki & Negueruela (2001); Okazaki et al (2011)). We note that the asymmetric wing could also be explained by the presence of ejecta outflowing from the decretion disk.…”

Large-scale flow dynamics and radiation in pulsarγ-ray binaries

“…Outside the equatorial disk, the radiatively driven wind in Be stars is most likely polar. Such a configuration of the two stellar flows probably makes the geometry of the colliding wind region quite complex, enhancing the development of instabilities in the shocked-flow contact discontinuity (for simulations of this scenario on binary system scales, see Romero et al 2007 andOkazaki et al 2011). The shocked disk material has a much larger density than the light polar wind.…”