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Probing the nature of the low state in the extreme ultraluminous X-ray pulsar NGC 5907 ULX1

Probing the nature of the low state in the extreme ultraluminous X-ray pulsar NGC 5907 ULX1
Probing the nature of the low state in the extreme ultraluminous X-ray pulsar NGC 5907 ULX1
NGC 5907 ULX1 is the most luminous ultra-luminous X-ray pulsar (ULXP) known to date, reaching luminosities in excess of 1e41 erg/s. The pulsar is known for its fast spin-up during the on-state. Here, we present a long-term monitoring of the X-ray flux and the pulse period between 2003-2022. We find that the source was in an off- or low-state between mid-2017 to mid-2020. During this state, our pulse period monitoring shows that the source had spun down considerably. We interpret this spin-down as likely being due to the propeller effect, whereby accretion onto the neutron star surface is inhibited. Using state-of-the-art accretion and torque models, we use the spin-up and spin-down episodes to constrain the magnetic field. For the spin-up episode, we find solutions for magnetic field strengths of either around 1e12G or 1e13G, however, the strong spin-down during the off-state seems only to be consistent with a very high magnetic field, namely, >1e13G. This is the first time a strong spin-down is seen during a low flux state in a ULXP. Based on the assumption that the source entered the propeller regime, this gives us the best estimate so far for the magnetic field of NGC 5907 ULX1.
Accretion, accretion disks, Magnetic fields, Stars: neutron, X-rays: binaries, X-rays: individuals: NGC 5907 ULX1
0004-6361
Fuerst, F.
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Walton, D.J.
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Israel, G.L.
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Bachetti, M.
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Barret, D.
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Brightman, M.
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Earnshaw, H.P.
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Fabian, A.
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Heida, M.
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Imbrogno, M.
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Middleton, M.J.
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Pinto, C.
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Salvaterra, R.
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Roberts, T.P.
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Rodríguez Castillo, G.A.
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Webb, N.
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Fuerst, F.
23883016-d1d1-4150-96c1-58b97d4c5160
Walton, D.J.
3cf6ea78-7dd5-4765-8c09-ba2af76f11e7
Israel, G.L.
a269c219-fe07-4b68-a93e-df57ffe1efdc
Bachetti, M.
06751b0e-e29a-44ae-b3d4-e9d70350ebcd
Barret, D.
d433f77a-8014-4933-83c7-1720f0561168
Brightman, M.
858d2a74-6dd4-4bcf-986d-8b8b8468af76
Earnshaw, H.P.
11572d2c-fb3f-4e4f-a87e-023edaf2b2f9
Fabian, A.
0c353376-f159-4129-b03e-d3993c0c5406
Heida, M.
fc66bb37-4c8d-4fc5-9af4-2e7438e45fcd
Imbrogno, M.
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Middleton, M.J.
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Pinto, C.
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Salvaterra, R.
8bfc09c8-fef4-407e-bfea-5a86e8a90043
Roberts, T.P.
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Rodríguez Castillo, G.A.
90f68c73-d6c3-448e-a3d2-57fb2945bfe6
Webb, N.
f13a0726-8f9f-4ab6-a3b6-8813629a958b

Fuerst, F., Walton, D.J., Israel, G.L., Bachetti, M., Barret, D., Brightman, M., Earnshaw, H.P., Fabian, A., Heida, M., Imbrogno, M., Middleton, M.J., Pinto, C., Salvaterra, R., Roberts, T.P., Rodríguez Castillo, G.A. and Webb, N. (2023) Probing the nature of the low state in the extreme ultraluminous X-ray pulsar NGC 5907 ULX1. Astronomy & Astrophysics, 672, [A140]. (doi:10.1051/0004-6361/202245048).

Record type: Article

Abstract

NGC 5907 ULX1 is the most luminous ultra-luminous X-ray pulsar (ULXP) known to date, reaching luminosities in excess of 1e41 erg/s. The pulsar is known for its fast spin-up during the on-state. Here, we present a long-term monitoring of the X-ray flux and the pulse period between 2003-2022. We find that the source was in an off- or low-state between mid-2017 to mid-2020. During this state, our pulse period monitoring shows that the source had spun down considerably. We interpret this spin-down as likely being due to the propeller effect, whereby accretion onto the neutron star surface is inhibited. Using state-of-the-art accretion and torque models, we use the spin-up and spin-down episodes to constrain the magnetic field. For the spin-up episode, we find solutions for magnetic field strengths of either around 1e12G or 1e13G, however, the strong spin-down during the off-state seems only to be consistent with a very high magnetic field, namely, >1e13G. This is the first time a strong spin-down is seen during a low flux state in a ULXP. Based on the assumption that the source entered the propeller regime, this gives us the best estimate so far for the magnetic field of NGC 5907 ULX1.

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Accepted/In Press date: 23 January 2023
Published date: 12 April 2023
Additional Information: Funding Information: The authors would like to thank the referee for their useful feedback, which helped to improve the final version of the manuscript. D.J.W. acknowledges support from an STFC Ernest Rutherford Fellowship. T.P.R. acknowledges support from the Science and Technology Facilities Council (STFC) as part of the consolidated grant award ST/000244/1. This research has also made use of data obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States, and has also made use of public data from the Swift data archive. We thank Kyle Parfrey for the useful discussion. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. Publisher Copyright: © 2023 The Authors.
Keywords: Accretion, accretion disks, Magnetic fields, Stars: neutron, X-rays: binaries, X-rays: individuals: NGC 5907 ULX1

Identifiers

Local EPrints ID: 477446
URI: http://eprints.soton.ac.uk/id/eprint/477446
ISSN: 0004-6361
PURE UUID: 6b5b4bbb-2f80-4cef-a01c-69af33aa25e3

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Date deposited: 06 Jun 2023 17:05
Last modified: 17 Mar 2024 02:18

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Contributors

Author: F. Fuerst
Author: D.J. Walton
Author: G.L. Israel
Author: M. Bachetti
Author: D. Barret
Author: M. Brightman
Author: H.P. Earnshaw
Author: A. Fabian
Author: M. Heida
Author: M. Imbrogno
Author: M.J. Middleton
Author: C. Pinto
Author: R. Salvaterra
Author: T.P. Roberts
Author: G.A. Rodríguez Castillo
Author: N. Webb

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