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

Hemphill, Paul B. and Rothschild, Richard E. and Fürst, Felix and Grinberg, Victoria and Klochkov, Dmitry and Kretschmar, Peter and Pottschmidt, Katja and Staubert, Rüdiger and Wilms, Jörn (2016) Evidence for an evolving cyclotron line energy in 4U 1538−522. Monthly Notices of the Royal Astronomical Society, 458 (3). pp. 2745-2761. ISSN 0035-8711. http://resolver.caltech.edu/CaltechAUTHORS:20160603-090404736

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Abstract

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.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1093/mnras/stw470DOIArticle
http://mnras.oxfordjournals.org/content/458/3/2745.abstractPublisherArticle
http://arxiv.org/abs/1603.02198arXivDiscussion Paper
Additional Information:© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 February 25. Received 2016 February 4. In original form 2015 December 3. First published online March 3, 2016. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. Our analysis makes heavy use of a collection of ISIS scripts provided by ECAP/Remeis Observatory and MIT, which can be found at http://www.sternwarte.uni-erlangen.de/isis/. Support for VG was provided by NASA through the Smithsonian Astrophysical Observatory (SAO) contract SV3-73016 to MIT for Support of the Chandra X-Ray Center (CXC) and Science Instruments; CXC is operated by SAO on behalf of NASA under contract NAS8-03060.
Funders:
Funding AgencyGrant Number
Smithsonian Astrophysical ObservatorySV3-73016
NASANAS8-03060
Subject Keywords:accretion, accretion discs stars: magnetic field pulsars: individual: 4U 1538−522 X-rays: binaries X-rays: stars
Record Number:CaltechAUTHORS:20160603-090404736
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160603-090404736
Official Citation:Paul B. Hemphill, Richard E. Rothschild, Felix Fürst, Victoria Grinberg, Dmitry Klochkov, Peter Kretschmar, Katja Pottschmidt, Rüdiger Staubert, and Jörn Wilms Evidence for an evolving cyclotron line energy in 4U 1538−522 MNRAS (May 21, 2016) Vol. 458 2745-2761 doi:10.1093/mnras/stw470 first published online March 3, 2016
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67641
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:03 Jun 2016 16:18
Last Modified:03 Jun 2016 16:18

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