Abstract
A0535 + 26 is the prototype object of the hard spectrum, pulsating X-ray transients associated with Be companions. Our analysis of its 1969–79 X-ray (3–12 keV) time history, measured by the Vela 5B satellite, shows a period of 111.0 ± 0.4 days, confirming the suggestion of Nagase et al.1. A likely explanation for the period is binary motion in a wide orbit. ‘Giant’ outbursts (flux ≥ 1 Crab ≃ 40 Vela counts s−1) observed in 1975 and 1980 are not in phase with the 111-day maxima. The source became significantly more active after the 1975 event, averaging ≃3 Vela counts s−1, compared with ≃0.5 counts s−1 before. The latter count rate corresponds to a time averaged X-ray luminosity of 1×1035 erg s−1 at 1.3 kpc. The mass loss rate from the companion, HDE245770, required to power this luminosity by wind accretion is 10−5 M⊙ yr−1, which is excessive for a B0V star. It is more likely that the transferred matter is lost from the equatorial region of the rapidly rotating B star.
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Priedhorsky, W., Terrell, J. 111-day periodicity of X-ray transient A0535 + 26. Nature 303, 681–683 (1983). https://doi.org/10.1038/303681a0
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DOI: https://doi.org/10.1038/303681a0
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