Boon and bane of studying the multiple cyclotron source 4U 0115+63

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https://pos.sissa.it/176/020/

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https://doi.org/10.22323/1.176.0020
 http://hdl.handle.net/11603/29794

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
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https://orcid.org/0000-0002-4656-6881

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2013-07-18

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conference papers and proceedings
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Mueller, Sebastian, Carlo Ferrigno, Matthias Kühnel, Gabriele Schoenherr, Peter A. Becker, Michael T. Wolff, Dominik Hertel, et al. “Boon and Bane of Studying the Multiple Cyclotron Source 4U 0115+63.” In Proceedings of An INTEGRAL View of the High-Energy Sky (the First 10 Years) - 9th INTEGRAL Workshop and Celebration of the 10th Anniversary of the Launch — PoS(INTEGRAL 2012), 176:020. SISSA Medialab, 2013. https://doi.org/10.22323/1.176.0020.

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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract

We present a study of RXTE and INTEGRAL spectra of the transient 3.6 s X-ray pulsar 4U 0115+634 taken during a giant outburst in 2008 March/April. The spectra can be almost equally well modeled by two different semi-empirical continuum models, modified by an Fe Kα fluorescence line, interstellar absorption, and cyclotron resonance scattering features (CRSFs) located at ∼10.7, 21.8, 35.5, 46.7, and 59.7 keV. One of these two models, the so called NPEX model, leads to an anticorrelation between the centroid energy of the fundamental CRSF E0 and the X-ray flux FX, in agreement with previous works. The other model, consisting of a simple exponentially cutoff power law modified by a Gaussian emission feature around 10 keV, however, leads to a constant value for E0 for the observed fluxes and a comparatively narrow line shape. We show that the cyclotron line model component resulting from the NPEX fits rather contribute to the broadband continuum model. We conclude that the previously reported anticorrelation is probably due to an artifact of the particular modeling of the continuum.