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SMC X-3: the closest ultraluminous X-ray source powered by a neutron star with non-dipole magnetic field

Tsygankov, S. S. and Doroshenko, V. and Lutovinov, A. A. and Mushtukov, A. A. and Poutanen, J. (2017) SMC X-3: the closest ultraluminous X-ray source powered by a neutron star with non-dipole magnetic field. Astronomy and Astrophysics, 605 . Art. No. A39. ISSN 0004-6361. doi:10.1051/0004-6361/201730553.

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Aims. The magnetic field of accreting neutron stars determines their overall behavior including the maximum possible luminosity. Some models require an above-average magnetic field strength (≳10^(13) G) in order to explain super-Eddington mass accretion rate in the recently discovered class of pulsating ultraluminous X-ray sources (ULX). The peak luminosity of SMC X-3 during its major outburst in 2016–2017 reached ~2.5 × 10^(39) erg s^(-1) comparable to that in ULXs thus making this source the nearest ULX-pulsar. Determination of the magnetic field of SMC X-3 is the main goal of this paper. Methods. SMC X-3 belongs to the class of transient X-ray pulsars with Be optical companions, and exhibited a giant outburst in July 2016–March 2017. The source has been observed over the entire outburst with the Swift/XRT and Fermi/GBM telescopes, as well as the NuSTAR observatory. Collected data allowed us to estimate the magnetic field strength of the neutron star in SMC X-3 using several independent methods. Results. Spin evolution of the source during and between the outbursts, and the luminosity of the transition to the so-called propeller regime in the range of (0.3–7) × 10^(35) erg s^(-1) imply a relatively weak dipole field of (1–5) × 10^(12) G. On the other hand, there is also evidence for a much stronger field in the immediate vicinity of the neutron star surface. In particular, transition from super- to sub-critical accretion regime associated with the cease of the accretion column and very high peak luminosity favor a field that is an order of magnitude stronger. This discrepancy makes SMC X-3 a good candidate for possessing significant non-dipolar components of the field, and an intermediate source between classical X-ray pulsars and accreting magnetars which may constitute an appreciable fraction of ULX population.

Item Type:Article
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URLURL TypeDescription Paper
Tsygankov, S. S.0000-0002-9679-0793
Poutanen, J.0000-0002-0983-0049
Additional Information:© 2017 ESO. Article published by EDP Sciences. Received 3 February 2017; Accepted 16 May 2017; Published online 05 September 2017. This work was supported by the Russian Science Foundation grant 14-12-01287 (S.S.T., A.A.L., A.A.M.), the Foundations’ Professor Pool, the Finnish Cultural Foundation and the Academy of Finland grant 268740 (J.P.). We also acknowledge the support from the COST Action MP1304.
Subject Keywords:accretion, accretion disks – magnetic fields – X-rays: binaries – X-rays: individuals: SMC X-3
Record Number:CaltechAUTHORS:20170206-090626010
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Official Citation:SMC X-3: the closest ultraluminous X-ray source powered by a neutron star with non-dipole magnetic field. S. S. Tsygankov, V. Doroshenko, A. A. Lutovinov, A. A. Mushtukov and J. Poutanen. A&A, 605 (2017) A39. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74067
Deposited By: Joy Painter
Deposited On:06 Feb 2017 17:32
Last Modified:11 Nov 2021 05:24

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