Evidence for an evolving cyclotron line energy in 4U 1538-522

Journal article
(Original article)

Publication Details

Author(s): Hemphill PB, Rothschild RE, Furst F, Grinberg V, Klochkov D, Kretschmar P, Pottschmidt K, Staubert R, Wilms J
Journal: Monthly Notices of the Royal Astronomical Society
Publisher: Oxford University Press
Publication year: 2016
Volume: 458
Journal issue: 3
Pages range: 2745-2761
ISSN: 0035-8711
eISSN: 1365-2966


We have performed a full time and luminosity-resolved spectral analysis of the high-mass X-ray binary 4U 1538-522 using the available RXTE, INTEGRAL, and Suzaku data, examining both phase-averaged and pulse-phase-constrained data sets and focusing on the behaviour of the cyclotron resonance scattering feature (CRSF). No statistically significant trend between the energy of the CRSF and luminosity is observed in the combined data set. However, the CRSF energy appears to have increased by ~1.5 keV in the ~8.5 yr between the RXTE and Suzaku measurements, with Monte Carlo simulations finding the Suzaku measurement 4.6σ above the RXTE points. Interestingly, the increased Suzaku CRSF energy is much more significant and robust in the pulse-phase-constrained spectra from the peak of the main pulse, suggesting a change that is limited to a single magnetic pole. The seven years of RXTE measurements do not show any strongly significant evolution with time on their own. We discuss the significance of the CRSF's behaviour with respect to luminosity and time in the context of historical observations of this source as well as recent observational and theoretical work concerning the neutron star accretion column, and suggest some mechanisms by which the observed change over time could occur.

FAU Authors / FAU Editors

Wilms, Jörn Prof. Dr.
Professur für Astronomie und Astrophysik

External institutions with authors

California Institute of Technology (Caltech)
Eberhard Karls Universität Tübingen
European Space Astronomy Centre (ESAC)
Massachusetts Institute of Technology (MIT)
University of California, San Diego
University of Maryland, Baltimore County

How to cite

Hemphill, P.B., Rothschild, R.E., Furst, F., Grinberg, V., Klochkov, D., Kretschmar, P.,... Wilms, J. (2016). Evidence for an evolving cyclotron line energy in 4U 1538-522. Monthly Notices of the Royal Astronomical Society, 458(3), 2745-2761. https://dx.doi.org/10.1093/mnras/stw470

Hemphill, Paul B., et al. "Evidence for an evolving cyclotron line energy in 4U 1538-522." Monthly Notices of the Royal Astronomical Society 458.3 (2016): 2745-2761.


Last updated on 2019-26-07 at 09:33