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Long-term properties of accretion discs in X-ray binaries - III. A search for spin-superorbital correlation in SMC X-1

Long-term properties of accretion discs in X-ray binaries - III. A search for spin-superorbital correlation in SMC X-1
Long-term properties of accretion discs in X-ray binaries - III. A search for spin-superorbital correlation in SMC X-1

Due to long-term X-ray monitoring, a number of interacting binaries are now known to show X-ray periodicities on time-scales of tens to hundreds of binary orbits. In some systems, precession of a warped accretion disc is the leading model to explain the superorbital modulation. The High-Mass X-ray Binary SMC X-1 showed two excursions in superorbital period (from ~60 d to ~45 d) during the 1996-2011 interval, suggesting that some characteristic of the accretion disc is varying on a time-scale of years. Because its behaviour as an X-ray pulsar has also been intensively monitored, SMC X-1 offers the rare chance to track changes in both the accretion disc and pulsar behaviours over the same interval. We have used archival X-ray observations of SMC X-1 to investigate whether the evolution of its superorbital variation and pulse period are correlated. We use the 16-year data set afforded by the RXTE All-Sky Monitor to trace the behaviour of the warped accretion disc in this system, and use published pulse-period histories to trace the behaviour of the pulsar. While we cannot claim a strong detection of correlation, the first superorbital period excursion near MJD 50 800 does coincide with structure in SMC X-1's pulse-period history. Our preferred interpretation is that the superorbital period excursion coincides with a change in the long-term spin-up rate of the SMC X-1 pulsar. In this scenario, the pulsar and the accretion disc are both responding to a change in the accretion flow, which the disc itself may regulate.

Accretion, Accretion discs, Pulsars: individual: SMC X-1, X-rays: binaries
0035-8711
337-350
Dage, Kristen C.
e40ee1bb-898d-4f6c-b902-7f3620f611aa
Clarkson, William I.
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Charles, Philip A.
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Laycock, Silas G.T.
d4e5bb78-7038-4e42-aaf5-9fdc20f60037
Shih, I. Chun
e2906657-21ab-4615-a1c6-fb68c9375a31
Dage, Kristen C.
e40ee1bb-898d-4f6c-b902-7f3620f611aa
Clarkson, William I.
6f676af8-c993-408d-9856-2b7713692502
Charles, Philip A.
0429b380-0754-4dc1-8def-885c7fa6a086
Laycock, Silas G.T.
d4e5bb78-7038-4e42-aaf5-9fdc20f60037
Shih, I. Chun
e2906657-21ab-4615-a1c6-fb68c9375a31

Dage, Kristen C., Clarkson, William I., Charles, Philip A., Laycock, Silas G.T. and Shih, I. Chun (2019) Long-term properties of accretion discs in X-ray binaries - III. A search for spin-superorbital correlation in SMC X-1. Monthly Notices of the Royal Astronomical Society, 482 (1), 337-350. (doi:10.1093/mnras/sty2572).

Record type: Article

Abstract

Due to long-term X-ray monitoring, a number of interacting binaries are now known to show X-ray periodicities on time-scales of tens to hundreds of binary orbits. In some systems, precession of a warped accretion disc is the leading model to explain the superorbital modulation. The High-Mass X-ray Binary SMC X-1 showed two excursions in superorbital period (from ~60 d to ~45 d) during the 1996-2011 interval, suggesting that some characteristic of the accretion disc is varying on a time-scale of years. Because its behaviour as an X-ray pulsar has also been intensively monitored, SMC X-1 offers the rare chance to track changes in both the accretion disc and pulsar behaviours over the same interval. We have used archival X-ray observations of SMC X-1 to investigate whether the evolution of its superorbital variation and pulse period are correlated. We use the 16-year data set afforded by the RXTE All-Sky Monitor to trace the behaviour of the warped accretion disc in this system, and use published pulse-period histories to trace the behaviour of the pulsar. While we cannot claim a strong detection of correlation, the first superorbital period excursion near MJD 50 800 does coincide with structure in SMC X-1's pulse-period history. Our preferred interpretation is that the superorbital period excursion coincides with a change in the long-term spin-up rate of the SMC X-1 pulsar. In this scenario, the pulsar and the accretion disc are both responding to a change in the accretion flow, which the disc itself may regulate.

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Accepted/In Press date: 17 September 2018
e-pub ahead of print date: 20 September 2018
Published date: 1 January 2019
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Keywords: Accretion, Accretion discs, Pulsars: individual: SMC X-1, X-rays: binaries

Identifiers

Local EPrints ID: 426949
URI: https://eprints.soton.ac.uk/id/eprint/426949
ISSN: 0035-8711
PURE UUID: 9661c099-457b-4fb1-a6e0-cc93989acb7f

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Date deposited: 18 Dec 2018 17:30
Last modified: 14 Aug 2019 16:37

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