The Surprising Long‐Term Evolution of the <scp>ULXP NGC</scp> 7793 <scp>P13</scp>

ABSTRACT The ultra‐luminous x‐ray pulsar (ULXP) NGC 7793 P13 has been regularly monitored with XMM‐Newton , NuSTAR , and Swift for the last 8 years. Here, we present the latest results of this monitoring campaign with respect to the pulse period evolution and spectral variability. We find that since the source recovered from an x‐ray low state in 2020–2022 the spin‐up rate has increased significantly compared with before the off‐state, even though the x‐ray luminosity has not shown an equivalent increase. We find that the x‐ray and optical/UV flux are anti‐correlated, and speculate that this variability might be driven by a large accretion disk, precessing at a super‐orbital period of 7–8 years. We study the spectral behavior in the XMM‐Newton and NuSTAR data, and find very little changes in the spectral shape, despite the large flux variability. This spectral consistency provides further indication that the observed flux variability is a geometric effect and not due to intrinsic changes of the accretion rate.