M51 ULX-7: superorbital periodicity and constraints on the neutron star magnetic field

G. Vasilopoulos, S. K. Lander, F. Koliopanos, C. D. Bailyn

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Abstract

In this work, we explore the applicability of standard theoretical models of accretion to the observed properties of M51 ULX-7. The spin-up rate and observed X-ray luminosity are evidence of a neutron star with a surface magnetic field of 2-7 x 10(13) G, rotating near equilibrium. Analysis of the X-ray light curve of the system (Swift/XRT data) reveals the presence of a similar to 39 d superorbital period. We argue that the superorbital periodicity is due to disc precession, and that material is accreted on to the neutron star at a constant rate throughout it. Moreover, by attributing this modulation to the free precession of the neutron star we estimate a surface magnetic field strength of 3-4 x 10(13) G. The agreement of these two independent estimates provide strong constraints on the surface polar magnetic field strength of the NS.

Original languageEnglish
Pages (from-to)4949-4959
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume491
Issue number4
Early online date11 Dec 2019
DOIs
Publication statusPublished - Feb 2020
Externally publishedYes

Keywords

  • stars: neutron
  • pulsars: individual: M51 ULX-7
  • galaxies: individual: M51
  • X-rays: binaries
  • X-RAY SOURCES
  • WARPED ACCRETION DISCS
  • SUPER-EDDINGTON ACCRETION
  • OPTICALLY THICK ENVELOPES
  • NGC 300 ULX1
  • FREE PRECESSION
  • LONG PERIODS
  • LIGHT CURVES
  • BLACK-HOLES
  • SMC X-1

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