XMM-Newton observations of CXOU J010043.1-721134: the first deep look at the soft X-ray emission of a magnetar

TL;DR

This study presents deep XMM-Newton observations of the magnetar candidate CXOU J010043.1-721134, revealing unique spectral features and providing the most constraining lower limit on a magnetar's radius, advancing understanding of magnetar emission.

Contribution

First detailed spectral analysis of CXOU J010043.1-721134 showing a two-blackbody model and successful application of resonant cyclotron scattering modeling.

Findings

Spectrum fits a two-blackbody model with specific temperatures and radii.

Provides the most constraining lower limit to a magnetar radius.

Successful application of a physical magnetosphere model.

Abstract

We present the analysis of six XMM-Newton observations of the Anomalous X-ray Pulsar CXOU J010043.1-721134, the magnetar candidate characterized by the lowest interstellar absorption. In contrast with all the other magnetar candidates, its X-ray spectrum cannot be fit by an absorbed power-law plus blackbody model. The sum of two (absorbed) blackbody components with kT1=0.30 keV and kT2=0.7 keV gives an acceptable fit, and the radii of the corresponding blackbody emission regions are R1=12.1 km and R2=1.7 km. The former value is consistent with emission from a large fraction of a neutron star surface and, given the well known distance of CXOU J010043.1-721134, that is located in the Small Magellanic Cloud, it provides the most constraining lower limit to a magnetar radius ever obtained. A more physical model, where resonant cyclotron scattering in the magnetar magnetosphere is taken into account, has also been successfully applied to this source.