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Simultaneous optical polarimetry and X-ray observations of the magnetic CV CP Tuc (AX J2315−592) |
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| Authors: | Gavin Ramsay S B Potter David A H Buckley Peter J Wheatley |
| Institution: | Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT; South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa; X-ray Astronomy Group, Department of Physics &Astronomy, University of Leicester, University Road, Leicester LE1 7RH |
| Abstract: | CP Tuc (AX J2315–592) shows a dip in X-rays which lasts for approximately half the binary orbit and is deeper in soft X-rays compared with hard X-rays. It has been proposed that this dip is due to the accretion stream obscuring the accretion region from view. If CP Tuc were a polar, as has been suggested, then the length of such a dip would make it unique amongst polars since in those polars in which a dip is seen in hard X-rays the dip lasts for only 0.1 of the orbit. We present optical polarimetry and RXTE observations of CP Tuc which show circular polarization levels of ～10 per cent and find evidence for only one photometric period. These data confirm CP Tuc as a polar. Our modelling of the polarization data implies that the X-ray dip is due to the bulk of the primary accretion region being self-eclipsed by the white dwarf. The energy dependence of the dip is due to a combination of this self-eclipse and also the presence of an X-ray temperature gradient over the primary accretion region. |
| Keywords: | binaries: eclipsing – stars: individual: CP Tuc (AX J2315–592)– stars: magnetic fields – novae cataclysmic variables – stars: variables: other – X‐rays: stars |