Spectroscopic comparison between ultraluminous X-ray sources and magnetar bursts

Understand

Nearby galaxies host ultra-luminous X-ray sources (ULXs), whose nature remains largely unknown.

• Until the discovery of the first ULX pulsar, M82 X-2, the mechanism powering the large luminosities of most ULXs was thought to be super-Eddington accretion onto black holes.
• The ULX pulsar clearly indicates that this hypothesis is not universal, and the question arises if other ULXs are as well powered by accretion onto neutron stars.
• One possibility to have highly super-Eddington luminosity is by reducing the opacity by strong magnetic fields as in magnetars, as proposed for M82 X-2.