Surface trapping and leakage of low-frequency g modes in rotating early-type stars – I. Qualitative analysis |
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| Authors: | R H D Townsend |
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| Institution: | Astronomical Institute 'Anton Pannekoek' and Center for High Energy Astrophysics, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, the Netherlands;Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ |
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| Abstract: | We summarize all the reported detections of, and upper limits to, the radio emission from persistent (i.e. non-transient) X-ray binaries. A striking result is a common mean observed radio luminosity from the black hole candidates (BHCs) in the low/hard X-ray state and the neutron star Z sources on the horizontal X-ray branch. This implies a common mean intrinsic radio luminosity to within a factor of 25 (or less, if there is significant Doppler boosting of the radio emission). Unless coincidental, these results imply a physical mechanism for jet formation that requires neither a black hole event horizon nor a neutron star surface. As a whole the populations of Atoll and X-ray pulsar systems are less luminous by factors of ?5 and ?10 at radio wavelengths than the BHCs and Z sources (while some Atoll sources have been detected, no high-field X-ray pulsar has ever been reliably detected as a radio source). We suggest that all of the persistent BHCs and the Z sources generate, at least sporadically, an outflow with physical dimensions  1012 cm; that is, significantly larger than the binary separations of most of the systems. We compare the physical conditions of accretion in each of the types of persistent X-ray binary and conclude that a relatively low ( 1010 G) magnetic field associated with the accreting object, and a high (0.1 Eddington) accretion rate and/or dramatic physical change in the accretion flow, are required for formation of a radio-emitting outflow or jet. |
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| Keywords: | binaries: close ISM: jets and outflows radio continuum: stars |
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