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Evolution of the Spin, Spectrum and Superorbital Period of the Ultraluminous X-Ray Pulsar M51 ULX7

Brightman, Murray and Bachetti, Matteo and Earnshaw, Hannah and Fürst, Felix and Heida, Marianne and Israel, Gian Luca and Pike, Sean and Stern, Daniel and Walton, Dominic J. (2022) Evolution of the Spin, Spectrum and Superorbital Period of the Ultraluminous X-Ray Pulsar M51 ULX7. Astrophysical Journal, 925 (1). Art. No. 18. ISSN 0004-637X. doi:10.3847/1538-4357/ac3829.

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M51 ULX7 is among a small group of known ultraluminous X-ray pulsars (ULXPs). The neutron star powering the source has a spin period of 2.8 s, orbits its companion star with a period of 2 days, and a superorbital period of 38 days is evident in its X-ray lightcurve. Here we present NuSTAR and XMM-Newton data on the source from 2019 obtained when the source was near its peak brightness. We detect the pulsations, having spun up at a rate of 3 ± 0.5 × 10⁻¹⁰ s s⁻¹ since they were previously detected in 2018. The data also provide the first high-quality broadband spectrum of the source. We find it to be very similar to that of other ULXPs, with two disk-like components, and a high-energy tail. When combined with XMM-Newton data obtained in 2018, we explore the evolution of the spectral components with superorbital phase, finding that the luminosity of the hotter component drives the superorbital flux modulation. The inclination the disk components appear to change with phase, which may support the idea that these superorbital periods are caused by disk precession. We also reexamine the superorbital period with 3 yr of Swift/XRT monitoring, finding that the period is variable, increasing from 38.2 ± 0.5 days in 2018–2019 to 44.2 ± 0.9 days in 2020–2021, which rules out alternative explanations for the superorbital period.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Brightman, Murray0000-0002-8147-2602
Bachetti, Matteo0000-0002-4576-9337
Earnshaw, Hannah0000-0001-5857-5622
Fürst, Felix0000-0003-0388-0560
Heida, Marianne0000-0002-1082-7496
Israel, Gian Luca0000-0001-5480-6438
Pike, Sean0000-0002-8403-0041
Stern, Daniel0000-0003-2686-9241
Walton, Dominic J.0000-0001-5819-3552
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 July 23; revised 2021 November 8; accepted 2021 November 8; published 2022 January 21. We thank the referee for their thorough review of our paper which improved it. This work was also supported under NASA Contract No. NNG08FD60C. NuSTAR is a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS), jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). This work was also based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. We wish to thank the Swift P.I., Brad Cenko, for approving the target of opportunity requests we made to observe M51, as well as the rest of the Swift team for carrying them out. We also acknowledge the use of public data from the Swift data archive. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC. G.L.I. acknowledges funding from the Italian MIUR PRIN grant No. 2017LJ39LM. The work of D.S. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. D.J.W. acknowledges support from an STFC Ernest Rutherford Fellowship. Facilities: Swift(XRT) - Swift Gamma-Ray Burst Mission, NuSTAR - , XMM-Newton. - Software: NuSTARDAS, XMMSAS (Gabriel et al. 2004), XSPEC (Arnaud 1996), hendrics (Bachetti 2015).
Group:Space Radiation Laboratory, NuSTAR
Funding AgencyGrant Number
Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR)2017LJ39LM
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords:High mass x-ray binary stars; Ultraluminous x-ray sources; Pulsars; Neutron stars; Accretion
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: High mass x-ray binary stars (733); Ultraluminous x-ray sources (2164); Pulsars (1306); Neutron stars (1108); Accretion (14)
Record Number:CaltechAUTHORS:20220124-215321000
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Official Citation:Murray Brightman et al 2022 ApJ 925 18
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113088
Deposited By: George Porter
Deposited On:25 Jan 2022 15:20
Last Modified:25 Jan 2022 15:20

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