@article {41744,
	title = {M51 ULX-7: superorbital periodicity and constraints on the neutron star magnetic field},
	volume = {491},
	year = {2020},
	month = {2020/02/1},
	pages = {4949 - 4959},
	publisher = {OUP},
	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 {\texttimes} 10<SUP>13</SUP> G, rotating near equilibrium. Analysis of the X-ray light curve of the system (Swift/XRT data) reveals the presence of a \~{}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 {\texttimes} 10<SUP>13</SUP> G. The agreement of these two independent estimates provide strong constraints on the surface polar magnetic field strength of the NS.},
	keywords = {Astrophysics - High Energy Astrophysical Phenomena, galaxies: individual: M51, pulsars: individual: M51 ULX-7, stars: neutron, X-rays: binaries},
	isbn = {0035-8711},
	url = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.491.4949V},
	author = {Vasilopoulos, G. and Lander, S. K. and Koliopanos, F. and Bailyn, C. D.}
}
