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Explaining the asymmetric line profile in Cepheus X-4 with spectral variation across pulse phase

Bhargava, Yash and Bhalerao, Varun and Ballhausen, Ralf and Fürst, Felix and Pottschmidt, Katja and Tomsick, John A. and Wilms, Joern (2019) Explaining the asymmetric line profile in Cepheus X-4 with spectral variation across pulse phase. Monthly Notices of the Royal Astronomical Society, 482 (3). pp. 2902-2912. ISSN 0035-8711. doi:10.1093/mnras/sty2823.

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The high mass X-ray binary Cepheus X-4, during its 2014 outburst, showed evidence for an asymmetric cyclotron line in its hard X-ray spectrum. The 2014 spectrum provides one of the clearest cases of an asymmetric line profile among all studied sources with Cyclotron Resonance Scattering Features (CRSF). We present a phase-resolved analysis of NuSTAR and Suzaku data taken at the peak and during the decline phases of this outburst. We find that the pulse-phased resolved spectra are well-fit by a single, symmetric cyclotron feature. The fit parameters vary strongly with pulse phase: most notably the central energy and depth of the cyclotron feature, the slope of the power-law component, and the absorbing column density. We synthesise a ‘phase averaged’ spectrum using the best-fitting parameters for these individual pulse phases, and find that this combined model spectrum has a similar asymmetry in the cyclotron features as discovered in phase-averaged data. We conclude that the pulse phase resolved analysis with simple symmetric line profiles when combined can explain the asymmetry detected in the phase-averaged data.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bhargava, Yash0000-0002-5967-8399
Bhalerao, Varun0000-0002-6112-7609
Fürst, Felix0000-0003-0388-0560
Pottschmidt, Katja0000-0002-4656-6881
Tomsick, John A.0000-0001-5506-9855
Wilms, Joern0000-0003-2065-5410
Additional Information:© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2018 October 16. Received 2018 October 16; in original form 2018 April 5. Published: 22 October 2018. This work has 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). RB acknowledges support by DLR grant 50 OR 1410.
Subject Keywords:accretion, accretion discs – stars: neutron – X-rays: binaries – X-rays: individual (Cep X-4)
Issue or Number:3
Record Number:CaltechAUTHORS:20181023-115819195
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Official Citation:Yash Bhargava, Varun Bhalerao, Ralf Ballhausen, Felix Fürst, Katja Pottschmidt, John A Tomsick, Joern Wilms; Explaining the asymmetric line profile in Cepheus X-4 with spectral variation across pulse phase, Monthly Notices of the Royal Astronomical Society, Volume 482, Issue 3, 21 January 2019, Pages 2902–2912,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90366
Deposited By: Joy Painter
Deposited On:23 Oct 2018 19:37
Last Modified:16 Nov 2021 03:32

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