Speaker
Description
The discovery of coherent X-ray pulsations from ultraluminous X-ray sources (ULXs) provided the first concrete evidence that some ULXs host neutron stars (NSs) accreting at super-Eddington rates. This raises many new questions regarding the physics of super-Eddington accretion in the presence of strong magnetic fields and the fraction of the ULX population hosting NS accretors. One way to address these questions is to find more ULXs harbouring NSs, thereby increasing the population of known NS ULXs and enabling improved characterisation. In this talk, I report the discovery of a new candidate pulsating ultraluminous X-ray source (PULX) in NGC 5128 (Centaurus A). The candidate, 4XMM J132542.2–425943, is a known ULX and exhibits coherent pulsations at a frequency of 1.269 Hz in a single XMM-Newton observation at marginal significance. Unusually, the candidate displays a softer X-ray spectrum than other known PULXs. Identifying this candidate required a new approach to pulsation searches that accounts for the intrinsic randomisation employed during data reduction, which can introduce significant uncertainties in the strength of pulsation detections, potentially resulting in viable PULX candidates being unnecessarily discarded or vice versa. I will discuss this new search approach within the context of verifying the marginal signal from 4XMM J132542.2–425943 and how this approach can assist in expanding the population of NS ULXs.
