TRACKING THE ORBITAL ADVANCE OF THE FIRST ULTRALUMINOUS PULSAR M82 X-2

Ultraluminous Xray sources (ULXs) are Xray binaries radiating above theEddington luminosity. An increasing sample of ULXs are known to be powered byaccreting pulsars (PULXs), and it is currently unclear if their observedemission is amplified by strong radiation beaming or it denotes a genuinesuperEddington mass accretion rate. In the second case, the large mass transferrequired is expected to produce detectable effects on the binary orbit, whichwere tentatively detected in past observations. In this program, we use pulsartiming to track the orbital evolution of the first discovered PULX, M82 X2,producing a strong constraint on the mass transfer and finally discriminatebetween the beaming and the extreme superEddington models. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]