3XMM J004232.1+411314

[1] The compact object in this system has been unambiguously identified as a neutron star with a spin period of 3 seconds.

Using a subsequent NuSTAR observation, it was found that a single source was responsible for this emission, and optical HST images ruled out the presence of stars more massive than 3 solar masses in that direction.

By analysing archival data elaborated by the EXTraS project, this source showed dips (a short and linear decrease in the source luminosity, which returns subsequently at the previous luminosity level) in some observations.

The orbital period of the system is 4.01 hours, which is the same distance in time between two consecutive dips.

Using XMM-Newton observations of Andromeda Galaxy, this source luminosity stays in the range 0.8–2.8×1038 erg/s in the 0.2-12 keV photon energy band.