The common fundamental plane of X-ray emissions from pulsars and magnetars in quiescence

Magnetars are a unique class of neutron stars characterized by their incredibly strong magnetic fields. Unlike normal pulsars whose X-ray emission was driven by rotational energy loss, magnetars exhibit distinct X-ray emissions thought to be driven by their strong magnetic fields. Here, we present the results of magnetar X-ray spectra analysis in their quiescent state. In the sample studied in this paper, spectra of 17 magnetars can be fitted well with a model consisting of a power-law and a blackbody component. We found that the luminosity of the power-law component can be described by a function of blackbody temperature and emission-region radius. The same relation was seen in pulsars whose X-ray emission mechanism is thought to be different. The fact that these magnetars and pulsars share a common fundamental plane in the space spanned by non-thermal X-ray luminosity, surface temperature, and the radius of the thermally emitting region presents both challenges and hints to theoretical models for a complete comprehension of the magnetospheric emissions from these two classes of neutron stars.