IAR   05382
INSTITUTO ARGENTINO DE RADIOASTRONOMIA
Unidad Ejecutora - UE
artículos
Título:
Accretion vs colliding wind models for the gamma-ray binary LS I +61 303: an assessment
Autor/es:
G.E. ROMERO; A.T. OKAZAKI; M. ORELLANA; S.P. OWOCKI
Revista:
ASTRONOMY AND ASTROPHYSICS
Editorial:
ESO Sciences
Referencias:
Año: 2007 vol. 474 p. 15 - 22
ISSN:
0004-6361
Resumen:
Context: LS I +61 303 is a puzzling Be/X-ray binary with variable gamma-ray emission up to TeV energies. The nature of the compact object and the origin of the high-energy emission are unclear. One family of models invokes particle acceleration in shocks from the collision between the B-star wind and a relativistic pulsar wind,whereas another centers on a relativistic jet powered by accretion from theBe star decretion disc onto a black hole. Recent high-resolution radio observations showing a putative "cometary tail'' pointing away from the Be starnear periastron have been cited as support for the pulsar-wind model.Aims:We wish to carry out a quantitative assessment of these competing models.Methods:We apply a "Smoothed Particle Hydrodynamics'' (SPH) code in3D dynamical simulations for both the pulsar-wind-interaction and accretion-jet models. The former yields a dynamical description of the shape of the wind-windinteraction surface. The latter provides a dynamical estimation of the accretion rate under a variety of conditions, and how this varies with orbital phase.Results: The results allow critical evaluation of how the two distinct models confront the data in various wavebands.When one accounts for the 3D dynamical wind interaction under realistic constraints for the relative strength of the B-star and pulsar winds, the resulting form of the interaction front does not match the putative"cometary tail'' claimed from radio observations. On the other hand, dynamical simulations of the accretion-jet model indicate that the orbital phase variation of accretion power includes a secondary broad peak well away from periastron, thus providing a plausible way to explain the observed TeV gamma ray emission toward apastron.Conclusions:Contrary to previous claims, the colliding-wind model is not clearly established for LS I +61 303, whereas the accretion-jet model can reproduce many key characteristics, such as required energy budget, lightcurve, and spectrumof the observed TeV gamma-ray emission.