Evolution of the X-ray Properties of the Transient Magnetar XTE J1810-197

TL;DR

This study tracks the decade-long X-ray evolution of the transient magnetar XTE J1810-197, revealing flux decline, spectral stabilization, persistent hot-spot pulsations, and a possible absorption feature, indicating ongoing magnetar activity.

Contribution

It provides a comprehensive multi-epoch analysis of XTE J1810-197's X-ray properties, including spectral modeling and detection of a consistent absorption line, advancing understanding of magnetar evolution.

Findings

X-ray flux declined by a factor of 50 from 2003 to 2014.

The X-ray spectrum stabilized with multiple blackbody components.

A persistent 1.2 keV absorption line was detected at all epochs.

Abstract

We report on X-ray observations of the 5.54 s transient magnetar XTE J1810-197 using the XMM-Newton and Chandra observatories, analyzing new data from 2008 through 2014, and re-analyzing data from 2003 through 2007 with the benefit of these six years of new data. From the discovery of XTE J1810-197 during its 2003 outburst to the most recent 2014 observations, its 0.3-10 keV X-ray flux has declined by a factor of about 50 from 4.1E-11 to 8.1E-13 erg/cm^2/s. Its X-ray spectrum has now reached a steady state. Pulsations continue to be detected from a 0.3 keV thermal hot-spot that remains on the neutron star surface. The luminosity of this hot-spot exceeds XTE J1810-197's spin down luminosity, indicating continuing magnetar activity. We find that XTE J1810-197's X-ray spectrum is best described by a multiple component blackbody model in which the coldest 0.14 keV component likely originates from the entire neutron star surface, and the thermal hot-spot is, at different epochs, well described by an either one or two-component blackbody model. A 1.2 keV absorption line, possibly due to resonant proton scattering, is detected at all epochs. The X-ray flux of the hot spot decreased by approximately 20% between 2008 March and 2009 March, the same period during which XTE J1810-197 became radio quiet.