X-ray emission from isolated neutron stars: latest results from XMM-Newton, NICER and eROSITA

TL;DR

This paper reviews recent X-ray observations of various isolated neutron stars using XMM-Newton, NICER, and eROSITA, highlighting their thermal and non-thermal emission components and the challenges in understanding their diverse physical properties.

Contribution

It provides an overview of the latest observational results on different classes of isolated neutron stars, emphasizing new findings and the connection between various neutron star populations.

Findings

Detection of thermal X-ray emission from multiple INS classes.

Identification of new thermal INS candidates.

Insights into the relationship between different neutron star populations.

Abstract

The X-ray spectra of isolated neutron stars (INSs) typically include a thermal component, that comes from the cooling surface, and a non-thermal component, produced by highly-relativistic particles accelerated in the stellar magnetosphere. Hot spots from returning currents can also be detected. Middle-aged pulsars exhibit a mixture of these components, but other flavours of INSs, that show a large variety of physical parameters (such as spin period, magnetic field and age) emit only thermal X-rays. Typically, these stars are detected either in large serendipitous datasets from pointed X-ray observations or from searches in the data of all-sky surveys. The connection between these thermally-emitting INSs, the ordinary pulsars, and the new emergent class of pulsars characterized by a long period, that do not show X-ray emission despite their high magnetic field, is one of the current challenges in the study of neutron stars. In this contribution I will review the latest results on several objects belonging to various INS classes, such as the XDINS RX J1308.6+2127, the enigmatic Calvera, the long period PSR J0250+5854 and the new thermal INS candidates, obtained with the X-ray observatories XMM-Newton, NICER and eROSITA.