No anticorrelation between cyclotron line energy and X-ray flux in 4U 0115+634

Müller S, Ferrigno C, Kühnel M, Schoenherr G, Becker PA, Wolff MT, Hertel D, Schwarm FW, Grinberg V, Obst M, Caballero I, Pottschmidt K, Fuerst F, Kreykenbohm I, Rothschild RE, Hemphill P, Nunez SM, Torrejon JM, Klochkov D, Staubert R, Wilms J (2013)

Publication Status: Published

Publication Type: Journal article

Publication year: 2013

Journal

Publisher: EDP SCIENCES S A

Book Volume: 551

Article Number: ARTN A6

DOI: 10.1051/0004-6361/201220359

Abstract

We report on an outburst of the high mass X-ray binary 4U 0115+634 with a pulse period of 3.6 s in 2008 March/April as observed with RXTE and INTEGRAL. During the outburst the neutron star's luminosity varied by a factor of 10 in the 3-50 keV band. In agreement with earlier work we find evidence of five cyclotron resonance scattering features at similar to 10.7, 21.8, 35.5, 46.7, and 59.7 keV. Previous work had found an anticorrelation between the fundamental cyclotron line energy and the X-ray flux. We show that this apparent anticorrelation is probably due to the unphysical interplay of parameters of the cyclotron line with the continuum models used previously, e. g., the negative and positive exponent power law (NPEX). For this model, we show that cyclotron line modeling erroneously leads to describing part of the exponential cutoff and the continuum variability, and not the cyclotron lines. When the X-ray continuum is modeled with a simple exponentially cutoff power law modified by a Gaussian emission feature around 10 keV, the correlation between the line energy and the flux vanishes, and the line parameters remain virtually constant over the outburst. We therefore conclude that the previously reported anticorrelation is an artifact of the assumptions adopted in the modeling of the continuum.

Authors with CRIS profile

Involved external institutions

University of Geneva / Université de Genève (UNIGE) Switzerland (CH) George Mason University United States (USA) (US) U.S. Naval Research Laboratory United States (USA) (US) Leibniz Institute for Astrophysics Potsdam / Leibniz-Institut für Astrophysik Potsdam Germany (DE) University of Alicante / Universidad de Alicante / Universitat d'Alacant Spain (ES) Eberhard Karls Universität Tübingen Germany (DE) University of California, San Diego United States (USA) (US) University of Maryland United States (USA) (US) California Institute of Technology (Caltech) United States (USA) (US) University of Paris 7 - Denis Diderot / Université Paris VII Denis Diderot France (FR)

How to cite

APA:

Müller, S., Ferrigno, C., Kühnel, M., Schoenherr, G., Becker, P.A., Wolff, M.T.,... Wilms, J. (2013). No anticorrelation between cyclotron line energy and X-ray flux in 4U 0115+634. Astronomy & Astrophysics, 551. https://dx.doi.org/10.1051/0004-6361/201220359

MLA:

Müller, Sebastian, et al. "No anticorrelation between cyclotron line energy and X-ray flux in 4U 0115+634." Astronomy & Astrophysics 551 (2013).

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