Variable Absorption Line in XTE J1810-197

TL;DR

This study presents a long-term spectral and timing analysis of the transient magnetar XTE J1810-197, revealing variable absorption features and surface emission evolution through X-ray observations.

Contribution

It introduces a detailed analysis of the magnetar's spectral evolution and models the asymmetric absorption line, providing new insights into its surface and magnetospheric properties.

Findings

Absorption line at 1.1 keV is highly variable and asymmetric.

XTE J1810-197 shows higher pulsed emission above 1.5 keV.

Surface temperature and hot spot size evolve over time.

Abstract

We report the results of a long-term spectral and timing study of the first transient magnetar, XTE J1810-197 which was discovered in 2003 when its X-ray luminosity increased 100 fold. We fit X-ray spectra of all archival X-ray observations using a two-component blackbody model, where the cool component is most likely originating from the whole surface of the neutron star and the hot component is from a much smaller hot spot. We investigate the long-term evolution of the surface emission characteristics via tracing its surface temperature, apparent emitting area and the pulsed fraction. We evaluate the pulsed fraction in two energy intervals (<1.5 keV and >1.5 keV) and show that the XTE J1810-197 exhibits slightly higher pulsed emission at energies above 1.5 keV. We explore the characteristics of an absorption line detected around 1.1 keV. We find that the absorption feature is highly variable and its profile is asymmetric. To accurately represent this feature, we introduced an asymmetric Gaussian profile and quantified the level of asymmetry of the absorption feature.