Chandra probes the X-ray variability of M51 ULX-7: evidence of propeller transition and X-ray dips on orbital periods

Understand

We report on the temporal properties of the ULX pulsar M51 ULX-7 inferred from the analysis of the 2018-2020 Swift/XRT 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 NS is rotating near equilibrium.
• Alternatively, this off state could be related to a variable super-orbital period.
• Moreover, we report the discovery of periodic dips in the X-ray light curve that are associated with the binary orbital period.