CaltechAUTHORS
Published April 2023 | Version Published
Journal Article Open

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

Creators

  • 1. ROR icon European Space Astronomy Centre
  • 2. ROR icon University of Hertfordshire
  • 3. ROR icon University of Cambridge
  • 4. ROR icon Astronomical Observatory of Rome
  • 5. ROR icon Osservatorio Astronomico di Cagliari
  • 6. ROR icon Research Institute in Astrophysics and Planetology
  • 7. ROR icon California Institute of Technology
  • 8. ROR icon European Southern Observatory
  • 9. ROR icon University of Rome Tor Vergata
  • 10. ROR icon University of Southampton
  • 11. ROR icon Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano
  • 12. ROR icon Durham University

Abstract

NGC 5907 ULX1 is the most luminous ultra-luminous X-ray pulsar (ULXP) known to date, reaching luminosities in excess of 10⁴¹ erg s⁻¹. 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 and 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 10¹² G or 1013 G, however, the strong spin-down during the off-state seems only to be consistent with a very high magnetic field, namely, > 10¹³ G. 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.

Additional Information

© The Authors 2023. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication. 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.

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Additional details

Identifiers

Eprint ID
122145
Resolver ID
CaltechAUTHORS:20230705-476466000.6

Funding

Science and Technology Facilities Council (STFC)
ST/000244/1
ESA Member States

Dates

Created
2023-07-14
Created from EPrint's datestamp field
Updated
2023-07-14
Created from EPrint's last_modified field

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Space Radiation Laboratory