Speaker
Description
Quasi-periodic oscillations in the mHz range (mHz QPOs) have been detected in different X-ray binaries, hosting either a neutron star or a black hole. Nonetheless, the presence of mHz QPOs in a few ULXs was initially interpreted as the footprint of accreting intermediate-mass black holes. The detection of mHz QPOs first in M82 X-2, and then in M51 ULX-7 (two known pulsating ULXs), however, has demonstrated that this feature is also present in neutron stars shining at super-Eddington luminosities. Additionally, the similar properties of the QPOs in these two pulsating ULXs (a stable centroid frequency and rms) suggest that they could represent a peculiar feature of this class of extreme neutron stars. In this talk, I’ll present the results of our analysis on two other pulsating ULXs, namely NGC 7793 P13 and NGC 5907 ULX-1. We significantly detect a mHz QPO in multiple observations of NGC 7793 P13. I will show how the properties of this QPO align with those of M82 X-2 and M51 ULX-7, supporting the hypothesis that they represent a common feature among pulsating ULXs. I will also show how NGC 5907 ULX-1 could be the fourth pulsating ULX with a mHz QPO, although, in this case, the feature is only marginally detected. NewAthena, with its superb spectral capabilities and time resolution, is expected to help us better understand the link between the mHz QPOs observed in PULXs, their spin signals and the extreme accretion regime of super-Eddington sources.
