Date Presented:

2019/03/1

Abstract:

Ultra luminous X-ray Pulsars (ULXPs) are bright binary systems that host a Neutron Star (NS) and emit radiation in excess of the Eddington Limit expected for isotropic accretion. We have studies the spectral and spin properties of the ULXP NGC300 ULX1 through archival data, and have shown that its spin evolution from ~126 s down to 16 s is consistent with almost constant accretion between 2014 and 2018. Moreover, based on the 2018 Swift/XRT and NICER monitoring campaigns of the system we have concluded that even during an 100 d period where the observed flux drops by a factor of 20, the spin-up rate and thus the mass accretion rate remained almost constant. This can be explained only by invoking extreme X-ray absorption or obscuration due to extreme outflows from the accretion disk, or disk precession. Finally, an intriguing consequence is that assuming constant spin-up rate a NS spin reversal should have occurred around 2012.

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