From outburst to quiescence: the decay of the transient Anomalous X-ray Pulsar XTE J1810-197

TL;DR

This study analyzes the spectral and timing evolution of the transient magnetar XTE J1810-197 over four years, revealing a three-blackbody model fit, surface emission consistency, and a spectral feature indicating a strong magnetic field.

Contribution

It provides the first detailed spectral modeling of XTE J1810-197's outburst decay using a three-blackbody model and links spectral features to magnetic field estimates.

Findings

A three-blackbody model fits the spectral data better than previous models.

The coldest blackbody matches the pre-outburst surface emission.

A spectral feature at 1.1 keV suggests a magnetic field of about 2×10^14 G.

Abstract

XTE J1810-197 is the first transient Anomalous X-ray Pulsar ever discovered. Its highly variable X-ray flux allowed us to study the timing and spectral emission properties of a magnetar candidate over a flux range of about two orders of magnitude. We analyzed nine XMM-Newton observations of XTE J1810-197 collected over a four years baseline (September 2003 - September 2007). EPIC PN and MOS data were reduced and used for detailed timing and spectral analysis. Pulse phase spectroscopic studies were also carried out for observations with sufficiently high signal to noise. We find that: (i) a three blackbodies model reproduces the spectral properties of the source over the entire outburst statistically better than the two blackbodies model previously used in the literature, (ii) the coldest blackbody is consistent with the thermal emission from the whole surface, and has temperature and radius similar to those inferred from ROSAT observations before the outburst onset, (iii) there is a spectral feature around 1.1 keV during six consecutive observations (since March 2005); if due to proton resonant cyclotron scattering, it would imply a magnetic field of around 2E14 G. This is in a very good agreement with the value from the spin period measurements.