Evidence of a Cyclotron Feature in the Spectrum of the Anomalous X-Ray Pulsar 1RXS J170849–400910

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Published 2003 February 18 © 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A.
, , Citation Nanda Rea et al 2003 ApJ 586 L65 DOI 10.1086/374585

1538-4357/586/1/L65

Abstract

We report the results of a long observation of the anomalous X-ray pulsar 1RXS J170849-400910 obtained with the BeppoSAX satellite in 2001 August. The best-fit phase-averaged spectrum was an absorbed power-law plus blackbody model, with a photon index of Γ ~ 2.4 and a blackbody temperature of kTbb ~ 0.4 keV. We confirm the presence of significant spectral variations with the rotational phase of the pulsar. In the spectrum corresponding to the rising part of the pulse, we found an absorption-like feature at ~8.1 keV (a significance of 4 σ), most likely due to cyclotron resonant scattering. The centroid energy converts to a magnetic field of 9 × 1011 and 1.6 × 1015 G in the case of electrons and protons, respectively. If confirmed, this would be the first detection of a cyclotron feature in the spectrum of an anomalous X-ray pulsar.

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10.1086/374585