Analyzing X-ray pulsar profiles: geometry and beam pattern of A 0535+26

¹ CEA Saclay, DSM/IRFU/SAp – UMR AIM (7158) CNRS/CEA/Université P. Diderot, Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette, France
e-mail: isabel.caballero@cea.fr
² Institut für Physik und Technik, Universität Hildesheim, Marienburger Platz 22, 31141 Hildesheim, Germany
³ Institute für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Eberhard Karls Universität Tübingen, Sand 1, 72076 Tübingen, Germany
⁴ ISOC, European Space Astronomy Centre (ESAC), PO Box 78, 28691 Villanueva de la Cañada, Spain

Received: 2 April 2010
Accepted: 28 October 2010

Abstract

Aims. We applied a decomposition method to the energy dependent pulse profiles of the accreting binary pulsar A 0535+26, in order to identify the contribution of the two magnetic poles of the neutron star and to obtain constraints on the geometry of the system and on the beam pattern.

Methods. We analyzed pulse profiles obtained from RXTE observations in the X-ray regime. Basic assumptions of the method are that the asymmetry observed in the pulse profiles is caused by non-antipodal magnetic poles and that the emission regions have axisymmetric beam patterns.

Results. Constraints on the geometry of the pulsar and a possible solution of the beam pattern are given. We interpreted the reconstructed beam pattern in terms of a geometrical model of a hollow column plus a halo of scattered radiation on the neutron star surface, which includes relativistic light deflection.