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A comment on the colour-colour diagrams of low-mass X-ray binaries

Gierlinski, M.; Done, C.

Authors

M. Gierlinski



Abstract

Disc-accreting neutron stars come in two distinct varieties, atolls and Z sources, named after their differently shaped tracks on a colour–colour diagram as the source luminosity changes. Here we present analysis of three transient atoll sources showing that there is an additional branch in the colour–colour diagram of atoll sources which appears at very low luminosities. This new branch connects to the top of previously known C-shaped (atoll) path, forming a horizontal track where the average source flux decrease from right to left. This turns the C-shape into a Z. Thus both atolls and Z sources share the same topology on the colour–colour diagram and evolve in similar way, as a function of increasing averaged mass accretion rate. This strongly favours models in which the underlying geometry of these sources changes in similar ways. A possible scenario is one where the truncated disc approaches the neutron star when the accretion rate increases, but in the atolls the disc is truncated by evaporation (similarly to black holes), and in the Z sources it is truncated by the magnetic field.

Citation

Gierlinski, M., & Done, C. (2002). A comment on the colour-colour diagrams of low-mass X-ray binaries. Monthly Notices of the Royal Astronomical Society, 331(4), L47-L50. https://doi.org/10.1046/j.1365-8711.2002.05430.x

Journal Article Type Article
Publication Date 2002-04
Deposit Date Apr 28, 2008
Publicly Available Date Apr 28, 2008
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 331
Issue 4
Pages L47-L50
DOI https://doi.org/10.1046/j.1365-8711.2002.05430.x
Keywords Accretion, Accretion discs, X-rays, Binaries.

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