Possible Periodic Dips in the Pulsating Ultraluminous X-ray Source M51 ULX-7

Abstract

We report the discovery of possible periodic X-ray dips in a pulsating ultraluminous X-ray source, M51 ULX-7, with the archival Changra observations. With ~20 days of monitoring in the superorbital descending state, we discovered three dips with separations of ~2 and ~8 days via the Bayesian block technique. A phase-dispersion minimization and a ${\chi }^2$ test suggest that the dip is likely recurrent with a period of ~2 days, consistent with the orbital period of M51 ULX-7. We interpret the dip as an obscuring of the emission from the pulsar by the vertical structure on the stream-disk interaction region or the atmosphere of the companion star. Both interpretations suggest the viewing angle to be ~60 degrees. Given that the magnetic field of M51 ULX-7 is moderately high, $B\sim 10^{13}$ G, low geometric beaming with $b\lesssim 1/2$ is sufficient to explain the observed flux and the presence of dips. Obscuration of the stellar wind remains an alternative possible origin and further monitoring of the dips will be required.

8 pges, 4 figures, accepted for publication in ApJ

References in corpus (16)

• 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 coherent pulsations from the Ultraluminous X-ray Source NGC 7793 P13
• The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2
• ULX spectra revisited: Accreting, highly magnetized neutron stars as the engines of ultraluminous X-ray sources
• No magnetars in ULXs
• M51 ULX-7: super-orbital periodicity and constraints on the neutron star magnetic field
• Accretion Rates and Beaming in Ultraluminous X-ray Sources
• Modeling the light curves of ultraluminous X-ray sources as precession
• Joint H-alpha and X-ray Observations of Massive X-ray Binaries. I. The B-Supergiant System LS I +65 010 = 2S 0114+650
• Orbital and super-orbital periods in ULX pulsars, disc-fed HMXBs, Be/X-ray binaries and double-periodic variables
• Evolution of Spin, Orbital, and Superorbital Modulations of 4U 0114+650
• Parameterization studies of the properties of the X-ray dips for Low Mass X-ray binary X1916-053
• Investigating the mass of the intermediate mass black hole candidate HLX-1 with the SLIMBH model
• Chandra and XMM-Newton discovery of the transient X-ray pulsar in the nearby spiral galaxy NGC2403
• Chandra and Swift X-ray Observations of the X-ray Pulsar SMC X-2 During the Outburst of 2015

Cited by in corpus (6)

• Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1
• Three Ultraluminous X-ray Sources Hosted by Globular Clusters in NGC 1316
• Evolution of the spin, spectrum and super-orbital period of the ultraluminous X-ray pulsar M51 ULX7
• The Orbit of NGC 5907 ULX-1
• Spectral analysis of ultraluminous X-ray pulsars with models of X-ray pulsars
• Spectral and Temporal Properties of Ultra-luminous X-ray Source NGC 55 ULX1