Modeling the X-rays from the Central Compact Object PSR J1852+0040 in Kesteven 79: Evidence for a Strongly Magnetized Neutron Star

TL;DR

This study models X-ray pulsations from the neutron star PSR J1852+0040, revealing evidence for a strongly magnetized interior and a complex magnetic field structure that explains observed emission patterns and high surface temperature contrasts.

Contribution

It provides the first detailed modeling indicating the presence of a strongly magnetized interior in a CCO, supporting the hidden magnetic field hypothesis and explaining observed X-ray emission features.

Findings

Strong internal magnetic fields (>10^14 Gauss) are required to explain surface temperature contrasts.

A conventional polar cap model with a 'pencil plus fan' beam pattern suggests a magnetic field >10^12 Gauss.

No significant spin-phase-dependent absorption features were detected.

Abstract

I present modeling of the X-ray pulsations from the central compact object (CCO) PSR J1852+0040 in the Galactic supernova remnant Kesteven 79. In the context of thermal surface radiation from a rotating neutron star, a conventional polar cap model can reproduce the broad, large-amplitude X-ray pulse only with a "pencil plus fan" beam emission pattern, which is characteristic of strongly magnetized ($\gtrsim$10^12 Gauss) neutron star atmospheres, substantially stronger than the ~10^10 Gauss external dipole field inferred from the pulsar spin-down rate. This discrepancy can be explained by an axially displaced dipole. For other beaming patterns, it is necessary to invoke high-aspect-ratio emitting regions that are greatly longitudinally elongated, possibly due to an extremely offset dipole. For all assumed emission models, the existence of strong internal magnetic fields ($\gtrsim$10^14} Gauss) that preferentially channel internal heat to only a portion of the exterior is required to account for the implied high-temperature contrast across the stellar surface. This lends further observational evidence in support of the "hidden" strong magnetic field scenario, in which CCOs possess strong submerged magnetic fields that are substantially stronger than the external dipole field, presumably due to burial by fallback of supernova ejecta. I also conduct phase-resolved X-ray spectroscopy and find no evidence for prominent spin-phase-dependent absorption features that could be produced by cyclotron absorption/scattering.