Journal Article

Very long-term X-ray variations in LMXBs: solar cycle-like variations in the donor?

M. M. Kotze and P. A. Charles

in Monthly Notices of the Royal Astronomical Society: Letters

Published on behalf of The Royal Astronomical Society

Volume 402, issue 1, pages L16-L20
Published in print February 2010 |
Published online February 2010 | e-ISSN: 1745-3933 | DOI: http://dx.doi.org/10.1111/j.1745-3933.2009.00790.x

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Abstract

Long-term monitoring of Low Mass X-ray Binaries (LMXBs) by the All Sky Monitor on board the Rossi X-ray Timing Explorer now covers ∼13 yr and shows that certain LMXB types display very long-term (approximately several to tens of years) quasi-periodic modulations. These time-scales are much longer than any ‘super-orbital’ periods reported hitherto and likely have a different origin. We suggest here that they are due to long-term variations in the mass-transfer rate from the donor, which are a consequence of solar-like magnetic cycles that lead to Porb changes (as proposed by Richman, Applegate & Patterson for similar long-term variations in cataclysmic variables). Atoll sources display much larger amplitude modulations than Z sources over these time-scales, presumably because Z sources are Eddington limited and hence unable to respond as readily as Atoll sources to fluctuations in the mass-transfer rate from the donor.

Keywords: accretion, accretion discs; binaries: close; stars: magnetic fields; stars: neutron; novae, cataclysmic variables; X-rays: binaries

Journal Article.  3000 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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