Circinus X-1: survivor of a highly asymmetric supernova |
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Authors: | T. M. Tauris R. P. Fender E. P. J. van den Heuvel H. M. Johnston K. Wu |
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Affiliation: | Center for High-Energy Astrophysics and Sterrenkundig Instituut 'Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098-SJ Amsterdam, the Netherlands; Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia; Research Centre for Theoretical Astrophysics, School of Physics, University of Sydney, NSW 2006, Australia |
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Abstract: | We have analysed the kinematical parameters of Cir X-1 to constrain the nature of its companion star, the eccentricity of the binary and the pre-supernova parameter space. We argue that the companion is most likely to be a low-mass (≲2.0 M⊙) unevolved star and that the eccentricity of the orbit is 0.94±0.04. We have evaluated the dynamical effects of the supernova explosion and we find it must have been asymmetric. On average , we find that a kick of ∼740 km s−1 is needed to account for the recently measured radial velocity of +430 km s−1 (Johnston, Fender & Wu) for this extreme system. The corresponding minimum kick velocity is ∼500 km s−1. This is the largest kick needed to explain the motion of any observed binary system. If Cir X-1 is associated with the supernova remnant G321.9-0.3 then we find a limiting minimum age of this remnant of ∼60 000 yr. Furthermore, we predict that the companion star has lost ∼10 per cent of its mass as a result of stripping and ablation from the impact of the supernova shell shortly after the explosion. |
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Keywords: | stars: individual: Cir X-1 stars: neutron supernovae: general |
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