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NuSTAR observations of the X-ray pulsar LMC X-4: A constraint on the magnetic field and tomography of the system in the fluorescent iron line

Shtykovsky, A. E. and Lutovinov, A. A. and Arefiev, V. A. and Molkov, S. V. and Tsygankov, S. S. and Revnivtsev, M. G. (2017) NuSTAR observations of the X-ray pulsar LMC X-4: A constraint on the magnetic field and tomography of the system in the fluorescent iron line. Astronomy Letters, 43 (3). pp. 175-185. ISSN 1063-7737. doi:10.1134/S1063773717030069.

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We present the results of the spectral and timing analysis of the X-ray pulsar LMC X-4 based on data from the NuSTAR observatory in the broad X-ray energy range 3-79 keV. Along with a detailed analysis of the source's averaged spectrum, high-precision spectra corresponding to different phases of the neutron star spin cycle have been obtained for the first time. The Comptonization model is shown to describe best the source's spectrum, and the evolution of its parameters as a function of the pulse phase has been traced. For all spectra (the averaged and phase-resolved ones) in the energy range 5-55 keV we have searched for the cyclotron absorption line. The derived upper limit on the optical depth of the cyclotron line τ 0.15 (3 σ) points to the absence of this feature in the given energy range, which provides a constraint on the magnetic field of the neutron star: B < 3 × 10^(11) or > 6.5 × 10^(12) G. The latter constraint is consistent with the magnetic field estimate obtained by analyzing the pulsar's power spectrum, B ≅ 3 × 10^(13) G. Based on our analysis of the phase-resolved spectra, we have determined the delay between the emission peaks and the equivalent width of the fluorescent iron line. This delay depends on the orbital phase and is apparently associated with the travel time of photons between the emitting regions in the vicinity of the neutron star and the region where the flux is reflected (presumably in the inflowing stream or at the place of interaction between the stream and the outer edge of the accretion disk).

Item Type:Article
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URLURL TypeDescription Paper
Tsygankov, S. S.0000-0002-9679-0793
Alternate Title:Observations of the X-ray pulsar LMC X-4 with NuSTAR: limit on the magnetic field and tomography of the system in the fluorescent iron line
Additional Information:© 2017 Pleiades Publishing, Inc. Original Russian Text © A.E. Shtykovsky, A.A. Lutovinov, V.A. Arefiev, S.V. Molkov, S.S. Tsygankov, M.G. Revnivtsev, 2017, published in Pis’ma v Astronomicheskii Zhurnal, 2017, Vol. 43, No. 3, pp. 203–213. Received: 27 September 2016; First Online: 11 March 2017. This work was supported by the Russian Science Foundation (project no. 14-12-01287). We used data from the NuSTAR observatory, a project led by Caltech, funded by NASA, and managed by NASA/JPL. The data were reduced using the NUSTARDAS package, jointly developed by ASDC (Italy) and Caltech (USA). We thank R.A. Krivonos for his help in processing the NuSTAR data.
Subject Keywords:neutron stars, magnetic field, X-ray pulsars, LMC X-4
Issue or Number:3
Record Number:CaltechAUTHORS:20161027-094005120
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Official Citation:Shtykovsky, A.E., Lutovinov, A.A., Arefiev, V.A. et al. Astron. Lett. (2017) 43: 175.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71533
Deposited By: Joy Painter
Deposited On:27 Oct 2016 17:29
Last Modified:11 Nov 2021 04:46

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