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Monitoring observations of SMC X-1's excursions (MOOSE)-II: a new excursion accompanies spin-up acceleration

Monitoring observations of SMC X-1's excursions (MOOSE)-II: a new excursion accompanies spin-up acceleration
Monitoring observations of SMC X-1's excursions (MOOSE)-II: a new excursion accompanies spin-up acceleration

SMC X-1 is a high-mass X-ray binary showing superorbital modulation with an unstable period. Previous monitoring shows three excursion events in 1996–1998, 2005–2007, and 2014–2016. The superorbital period drifts from 60 to 40 d and then evolves back during an excursion. Here, we report a new excursion event of SMC X-1 in 2020–2021, indicating that the superorbital modulation has an unpredictable, chaotic nature. We trace the spin-period evolution and find that the spin-up rate accelerated 1 yr before the onset of this new excursion, which suggests a possible inside-out process connecting the spin-up acceleration and the superorbital excursion. This results in a deviation of the spin-period residual, similar to the behaviour of the first excursion in 1996–1998. In further analysis of the pulse profile evolution, we find that the pulsed fraction shows a long-term evolution and may be connected to the superorbital excursion. These discoveries deepen the mystery of SMC X-1 because they cannot be solely interpreted by the warped-disc model. Upcoming pointed observations and theoretical studies may improve our understanding of the detailed accretion mechanisms taking place.

astro-ph.HE, X-rays: binaries: individual: SMC X-1, stars: pulsars, accretion, accretion discs
1365-2966
3436-3442
Hu, Chin-Ping
38ee07da-9735-4ef2-9662-35d9f0dc747b
Dage, Kristen C.
e40ee1bb-898d-4f6c-b902-7f3620f611aa
Clarkson, William I.
6f676af8-c993-408d-9856-2b7713692502
Brumback, McKinley
c87f4650-6acd-46b0-85b3-70938fee5684
Charles, Philip A.
0429b380-0754-4dc1-8def-885c7fa6a086
Haggard, Daryl
29179449-da8e-4e11-9ea6-33f3e040e354
Hickox, Ryan C.
fa3d8d11-419b-4625-892f-7183fba98e8a
Mihara, Tatehiro
0664d0b2-43c2-4bbc-abed-6c40d02502d1
Bahramian, Arash
390154f6-92b9-4e9f-9c5e-2eeaec97460a
Karam, Rawan
800654bc-6d99-4a6a-a944-7d718ef41acd
Athukoralalage, Wasundara
48aadd58-312b-40ea-a2fd-2be28016023d
Altamirano, Diego
d5ccdb09-0b71-4303-9538-05b467be075b
Neilsen, Joey
9038bd94-0f91-4ff3-882e-a943be398aeb
Kennea, Jamie
fe98d3ce-4906-4b92-bb69-0e7891f73427
Hu, Chin-Ping
38ee07da-9735-4ef2-9662-35d9f0dc747b
Dage, Kristen C.
e40ee1bb-898d-4f6c-b902-7f3620f611aa
Clarkson, William I.
6f676af8-c993-408d-9856-2b7713692502
Brumback, McKinley
c87f4650-6acd-46b0-85b3-70938fee5684
Charles, Philip A.
0429b380-0754-4dc1-8def-885c7fa6a086
Haggard, Daryl
29179449-da8e-4e11-9ea6-33f3e040e354
Hickox, Ryan C.
fa3d8d11-419b-4625-892f-7183fba98e8a
Mihara, Tatehiro
0664d0b2-43c2-4bbc-abed-6c40d02502d1
Bahramian, Arash
390154f6-92b9-4e9f-9c5e-2eeaec97460a
Karam, Rawan
800654bc-6d99-4a6a-a944-7d718ef41acd
Athukoralalage, Wasundara
48aadd58-312b-40ea-a2fd-2be28016023d
Altamirano, Diego
d5ccdb09-0b71-4303-9538-05b467be075b
Neilsen, Joey
9038bd94-0f91-4ff3-882e-a943be398aeb
Kennea, Jamie
fe98d3ce-4906-4b92-bb69-0e7891f73427

Hu, Chin-Ping, Dage, Kristen C., Clarkson, William I., Brumback, McKinley, Charles, Philip A., Haggard, Daryl, Hickox, Ryan C., Mihara, Tatehiro, Bahramian, Arash, Karam, Rawan, Athukoralalage, Wasundara, Altamirano, Diego, Neilsen, Joey and Kennea, Jamie (2023) Monitoring observations of SMC X-1's excursions (MOOSE)-II: a new excursion accompanies spin-up acceleration. Monthly Notices of the Royal Astronomical Society, 520 (3), 3436-3442. (doi:10.1093/mnras/stad384).

Record type: Article

Abstract

SMC X-1 is a high-mass X-ray binary showing superorbital modulation with an unstable period. Previous monitoring shows three excursion events in 1996–1998, 2005–2007, and 2014–2016. The superorbital period drifts from 60 to 40 d and then evolves back during an excursion. Here, we report a new excursion event of SMC X-1 in 2020–2021, indicating that the superorbital modulation has an unpredictable, chaotic nature. We trace the spin-period evolution and find that the spin-up rate accelerated 1 yr before the onset of this new excursion, which suggests a possible inside-out process connecting the spin-up acceleration and the superorbital excursion. This results in a deviation of the spin-period residual, similar to the behaviour of the first excursion in 1996–1998. In further analysis of the pulse profile evolution, we find that the pulsed fraction shows a long-term evolution and may be connected to the superorbital excursion. These discoveries deepen the mystery of SMC X-1 because they cannot be solely interpreted by the warped-disc model. Upcoming pointed observations and theoretical studies may improve our understanding of the detailed accretion mechanisms taking place.

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2302.00260v1 - Accepted Manuscript
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Accepted/In Press date: 28 January 2023
e-pub ahead of print date: 6 February 2023
Published date: 15 February 2023
Additional Information: Publisher Copyright: © 2023 Oxford University Press. All rights reserved.
Keywords: astro-ph.HE, X-rays: binaries: individual: SMC X-1, stars: pulsars, accretion, accretion discs

Identifiers

Local EPrints ID: 476804
URI: http://eprints.soton.ac.uk/id/eprint/476804
ISSN: 1365-2966
PURE UUID: a01177e3-cbc3-4e8e-a085-c84feb5d45cc
ORCID for Diego Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 16 May 2023 16:56
Last modified: 17 Mar 2024 03:34

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Contributors

Author: Chin-Ping Hu
Author: Kristen C. Dage
Author: William I. Clarkson
Author: McKinley Brumback
Author: Daryl Haggard
Author: Ryan C. Hickox
Author: Tatehiro Mihara
Author: Arash Bahramian
Author: Rawan Karam
Author: Wasundara Athukoralalage
Author: Joey Neilsen
Author: Jamie Kennea

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