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Modelling the spin pulse profile of the isolated neutron star RX J0720.4-3125 observed with XMM-Newton

Cropper, M; Zane, S; Ramsay, G; Haberl, F; Motch, C; (2001) Modelling the spin pulse profile of the isolated neutron star RX J0720.4-3125 observed with XMM-Newton. ASTRON ASTROPHYS , 365 (1) L302 - L307. Green open access

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Abstract

We model the spin pulse intensity and hardness ratio profiles of the isolated neutron star RX J0720.4-3125 using XMM-Newton data. The observed variation is approximately sinusoidal with a peak-to-peak amplitude of 15%, and the hardness ratio is softest slightly before flux maximum. By using polar cap models we are able to derive maximum polar cap sizes and acceptable viewing geometries. The inferred sizes of the caps turn out to be more compatible with a scenario in which the neutron star is heated by accretion, and place limits on the magnetic field strength. The hardness ratio modulation can then be explained in terms of energy-dependent beaming effects, and this constrains the acceptable models of the emerging radiation to cases in which softer photons are more strongly beamed than harder photons. An alternative explanation in terms of spatially variable absorption co-rotating in the magnetosphere is also discussed.

Type: Article
Title: Modelling the spin pulse profile of the isolated neutron star RX J0720.4-3125 observed with XMM-Newton
Open access status: An open access version is available from UCL Discovery
Keywords: X-rays : stars, stars : neutron, stars : magnetic fields, individual : RX J0720.4-3125, RX J0720.4-3125, ATMOSPHERES, EMISSION, FIELDS
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/9410
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