The Magnetic Fields of Anomalous X-ray Pulsars

TL;DR

This paper presents a theoretical model for the atmospheres and magnetospheres of ultramagnetic neutron stars, successfully explaining the X-ray spectra of Anomalous X-ray Pulsars and supporting their classification as magnetars.

Contribution

It introduces a comprehensive physical model that accounts for atmospheric, magnetospheric, and gravitational effects to analyze AXP spectra, confirming their strong magnetic fields.

Findings

Spectra are well described by the model

Magnetic field strengths match spindown estimates

Supports magnetar classification

Abstract

Anomalous X-ray Pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spindowns. We have developed a theoretical model that takes into account processes in the atmospheres and magnetospheres of ultramagnetic neutron stars, as well as the effects of their strong gravitational fields on the observable properties. Using this model, we have analyzed the X-ray spectra of a number of AXPs. We find that in all cases, the X-ray spectra are described very well with this emission model. The spectroscopically measured magnetic field strengths of these sources are in close agreement with the values inferred from their spindown properties and provide independent evidence for their magnetar nature. The analysis of spectral data using this physical model also sheds light on the long-term evolution of AXPs.