Evolution of the spin, spectrum and super-orbital period of the ultraluminous X-ray pulsar M51 ULX7

Abstract

M51 ULX7 is among a small group of known ultraluminous X-ray pulsars (ULXP). The neutron star powering the source has a spin period of 2.8s, orbits its companion star with a period of 2 days, and a super-orbital 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$\pm 0.5\times 10^{-10}$ 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 super-orbital phase, finding that the luminosity of the hotter component drives the super-orbital flux modulation. The inclination the disk components appear to change with phase, which may support the idea that these super-orbital periods are caused by disk precession. We also reexamine the super-orbital period with 3 years of Swift/XRT monitoring, finding that the period is variable, increasing from 38.2$\pm 0.5$ days in 2018--2019 to 44.2$\pm 0.9$ days in 2020--2021, which rules out alternative explanations for the super-orbital period.

Accepted for publication in ApJ

References in corpus (29)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• An online repository of Swift/XRT light curves of GRBs
• An Ultraluminous X-ray Source Powered by An Accreting Neutron Star
• An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907
• Discovery of a 0.42-s pulsar in the ultraluminous X-ray source NGC 7793 P13
• PINT: A Modern Software Package for Pulsar Timing
• The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2
• Pulsator-like spectra from Ultraluminous X-ray sources and the search for more ultraluminous pulsars
• Ultraluminous X-Ray Sources
• Optically thick envelopes around ULXs powered by accreating neutron stars
• ULX spectra revisited: Accreting, highly magnetized neutron stars as the engines of ultraluminous X-ray sources
• A census of ultraluminous X-ray sources in the local Universe
• Spectral Changes in the Hyperluminous Pulsar in NGC 5907 as a Function of Super-Orbital Phase
• A 78 Day X-ray Period Detected from NGC 5907 ULX1 by Swift
• A new, clean catalogue of extragalactic non-nuclear X-ray sources in nearby galaxies
• Study of Recent outburst in the Be/X-ray binary RX J0209.6-7427 with AstroSat: A new ultraluminous X-ray pulsar in the Magellanic Bridge?
• Long-term X-ray spectral evolution of Ultraluminous X-ray sources: implications on the accretion flow geometry and the nature of the accretor
• The 2019 super-Eddington outburst of RX J0209.6-7427: Detection of pulsations and constraints on the magnetic field strength
• M51 ULX-7: super-orbital periodicity and constraints on the neutron star magnetic field
• NuSTAR and XMM-Newton observations of the extreme ultraluminous X-ray source NGC 5907 ULX1: A Vanishing Act
• A ~60-day super-orbital period originating from the ultraluminous X-ray pulsar in M82
• Modeling the light curves of ultraluminous X-ray sources as precession
• A new candidate pulsating ULX in NGC 7793
• Chandra probes the X-ray variability of M51 ULX-7: evidence of propeller transition and X-ray dips on orbital periods
• Extending the $Z_n^2$ and $H$ statistics to generic pulsed profiles
• Spectral evolution of the ultraluminous X-ray sources M82 X-1 and X-2
• Linking soft excess in ultraluminous X-ray sources with optically thick wind driven by supercritical accretion
• Monitoring the Superorbital Period Variation and the Spin Period Evolution of SMC X-1
• Possible Periodic Dips in the Pulsating Ultraluminous X-ray Source M51 ULX-7

Cited by in corpus (9)

• Reeling in the Whirlpool: the distance to M 51 clarified by Cepheids and the Type IIP SN 2005cs
• A new pulsating neutron star in the Ultraluminous X-ray source NGC 4559 X7?
• The ultraluminous X-ray source M81 X-6: a weakly magnetised neutron star with a precessing accretion disc?
• Monitoring Observations of SMC X-1's Excursions (MOOSE) I: Program Description and Initial High-State Spectral Results
• Constraining the evolution of the unstable accretion disk in SMC X-1 with NICER
• Spectral analysis of ultraluminous X-ray pulsars with models of X-ray pulsars
• The variability behavior of NGC 925 ULX-3
• Magnetic precession as a model for QPOs in PULXs: flat-top noise ULXs are different
• Pulsating ultraluminous X-ray sources: modeling the thermal emission and polarization properties