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NuStar Discovery of a cyclotron line in KS 1947+300

Fürst, Felix and Pottschmidt, Katja and Wilms, Jörn and Kennea, Jamie and Bachetti, Matteo and Bellm, Eric and Boggs, Steven E. and Chakrabarty, Deepto and Christensen, Finn E. and Craig, William W. and Hailey, Charles J. and Harrison, Fiona and Stern, Daniel and Tomsick, John A. and Walton, Dominic J. and Zhang, William (2014) NuStar Discovery of a cyclotron line in KS 1947+300. Astrophysical Journal Letters, 784 (2). Art. No. L40. ISSN 2041-8205. doi:10.1088/2041-8205/784/2/L40.

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We present a spectral analysis of three simultaneous Nuclear Spectroscopy Telescope Array and Swift/XRT observations of the transient Be-neutron star binary KS 1947+300 taken during its outburst in 2013/2014. These broadband observations were supported by Swift/XRT monitoring snapshots every three days, which we use to study the evolution of the spectrum over the outburst. We find strong changes of the power-law photon index, which shows a weak trend of softening with increasing X-ray flux. The neutron star shows very strong pulsations with a period of P ≈ 18.8 s. The 0.8–79 keV broadband spectrum can be described by a power law with an exponential cutoff and a blackbody component at low energies. During the second observation we detect a cyclotron resonant scattering feature at 12.5 keV, which is absent in the phase-averaged spectra of observations 1 and 3. Pulse phase-resolved spectroscopy reveals that the strength of the feature changes strongly with pulse phase and is most prominent during the broad minimum of the pulse profile. At the same phases the line also becomes visible in the first and third observation at the same energy. This discovery implies that KS 1947+300 has a magnetic field strength of B ≈ 1.1 × 10^(12) (1 + z) G, which is at the lower end of known cyclotron line sources.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fürst, Felix0000-0003-0388-0560
Pottschmidt, Katja0000-0002-4656-6881
Wilms, Jörn0000-0003-2065-5410
Kennea, Jamie0000-0002-6745-4790
Bachetti, Matteo0000-0002-4576-9337
Bellm, Eric0000-0001-8018-5348
Boggs, Steven E.0000-0001-9567-4224
Chakrabarty, Deepto0000-0001-8804-8946
Christensen, Finn E.0000-0001-5679-1946
Harrison, Fiona0000-0003-2992-8024
Stern, Daniel0000-0003-2686-9241
Tomsick, John A.0000-0001-5506-9855
Walton, Dominic J.0000-0001-5819-3552
Zhang, William0000-0002-1426-9698
Additional Information:© 2014 The American Astronomical Society. Received 2014 February 12; accepted for publication 2014 March 5; Published 2014 March 19; Issue 2 (2014 April 1). We would like to thank Matthias Kühnel, Ralf Ballhausen, Fritz Schwarm, and Peter Kretschmar for useful discussions. This work was supported under NASA contract No. NNG08FD60C, and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). This research has made use of ISIS functions provided by ECAP/Remeis observatory and MIT ( We thank the Deutsches Zentrum für Luft- und Raumfahrt for partial support under DLR grant 50 OR 1113. We thank the anonymous referee for useful comments. Facilities: NuSTAR, Swift
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Deutsches Zentrum für Luft-und Raumfahrt (DLR)50 OR 1113
Subject Keywords:accretion, accretion disks; radiation: dynamics; stars: neutron; X-rays: binaries; X-rays: individual (KS 1947+300)
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2014-64
Issue or Number:2
Record Number:CaltechAUTHORS:20140403-155508973
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Official Citation:Felix, F., Katja, P., Jörn, W., Jamie, K., Matteo, B., Eric, B., . . . William, Z. (2014). NuSTAR Discovery of a Cyclotron Line in KS 1947+300. The Astrophysical Journal Letters, 784(2), L40.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44649
Deposited On:04 Apr 2014 19:33
Last Modified:10 Nov 2021 16:54

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