No magnetars in ULXs

TLDR: In this article, the authors consider the current observed ensemble of pulsing ultraluminous X-ray sources (PULXs) and show that all of their observed properties (luminosity, spin period, and spin-up rate) are consistent with emission from magnetic neutron stars with fields in the usual range 1011-1013G.

Abstract: We consider the current observed ensemble of pulsing ultraluminous X-ray sources (PULXs). We show that all of their observed properties (luminosity, spin period, and spin-up rate) are consistent with emission from magnetic neutron stars with fields in the usual range 1011--1013G⁠, which is collimated (‘beamed’) by the outflow from an accretion disc supplied with mass at a super-Eddington rate, but ejecting the excess, in the way familiar for other (non-pulsing) ULXs. The observed properties are inconsistent with magnetar-strength fields in all cases. We point out that all proposed pictures of magnetar formation suggest that they are unlikely to be members of binary systems, in agreement with the observation that all confirmed magnetars are single. The presence of magnetars in ULXs is therefore improbable, in line with our conclusions above.