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Published March 1, 2021 | Accepted Version + Published
Journal Article Open

Chandra Probes the X-Ray Variability of M51 ULX-7: Evidence of Propeller Transition and X-Ray Dips on Orbital Periods

Abstract

We report on the temporal properties of the ultraluminous X-ray (ULX) pulsar M51 ULX-7 inferred from the analysis of the 2018–2020 Swift/X-ray Telescope monitoring data and archival Chandra data obtained over a period of 33 days in 2012. We find an extended low flux state, which might be indicative of propeller transition, lending further support to the interpretation that the neutron star is rotating near equilibrium. Alternatively, this off-state could be related to a variable superorbital period. Moreover, we report the discovery of periodic dips in the X-ray light curve that are associated with the binary orbital period. The presence of the dips implies a configuration where the orbital plane of the binary is closer to an edge-on orientation, and thus demonstrates that favorable geometries are not necessary in order to observe ULX pulsars. These characteristics are similar to those seen in prototypical X-ray pulsars such as Her X-1 and SMC X-1 or other ULX pulsars such as NGC 5907 ULX1.

Additional Information

© 2021. The American Astronomical Society. Received 2020 November 18; revised 2021 January 8; accepted 2021 January 8; published 2021 March 4. The authors would like to thank the anonymous referee for their comments and suggestions that helped improve the manuscript. We would like to thank the organizers of the "Chandra Frontiers in Time-Domain Science" meeting that was held virtually in 2020 October. Presentation of M51 monitoring data and discussions that followed resulted in the current work. G.V. acknowledges support by NASA grant Nos. 80NSSC20K1107, 80NSSC20K0803 and 80NSSC21K0213. Software: HEASoft v6.26, CIAO v4.12.1, Python v3.7.3, IDL®.

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Published - Vasilopoulos_2021_ApJ_909_50.pdf

Accepted Version - 2102.07996.pdf

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Additional details

Created:
August 22, 2023
Modified:
October 23, 2023