SIMBAD references

2006MNRAS.366..727Z - Mon. Not. R. Astron. Soc., 366, 727-738 (2006/March-1)

Unveiling the thermal and magnetic map of neutron star surfaces though their X-ray emission: method and light-curve analysis.


Abstract (from CDS):

Recent Chandra and XMM-Newton observations of a number of X-ray `dim' pulsating neutron stars have revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is relatively large (pulsed fractions in the range ∼12-35 per cent), the pulse shape is often non-sinusoidal, and the hard X-ray colour appears to be anticorrelated in phase with the total emission. Moreover, the prototype of this class, RX J0720.4-3125, has been found to undergo rather sensible changes in both its spectral and timing properties over a time-scale of a few years. All these new findings seem difficult to reconcile with the standard picture of a cooling neutron star endowed with a purely dipolar magnetic field, at least if surface emission is produced in an atmosphere on top of the crust. In this paper we explore how a dipolar+quadrupolar star-centred field influences the properties of the observed light curves. The phase-resolved spectrum has been evaluated accounting for both radiative transfer in a magnetized atmosphere and general relativistic ray-bending. We computed over 78000 light curves, varying the quadrupolar components and the viewing geometry. A comparison of the data with our model indicates that higher-order multipoles are required to reproduce the observations.

Abstract Copyright: 2006 The Authors. Journal compilation © 2006 RAS

Journal keyword(s): stars: individual: RX J0720.4-3125 - stars: individual: RX J0420.0-5022 - stars: individual: RX J0806.4-4123 - stars: individual: RBS 1223 - stars: individual: RBS 1774 - stars: neutron

Simbad objects: 6

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