On the X-Ray Light Curve, Pulsed-Radio Emission, and Spin Frequency Evolution of the Transient Anomalous X-Ray Pulsar Xte J1810--197 During its X-Ray Outburst

TL;DR

This paper explains the X-ray outburst, spin evolution, and pulsed-radio emission of the transient AXP XTE J1810-197 using a fallback disk model, linking low accretion power to radio emission emergence.

Contribution

It presents a unified model connecting the X-ray light curve, spin changes, and radio emission of XTE J1810-197 through fallback disk evolution and disk-magnetosphere interactions.

Findings

X-ray outburst explained by a fallback disk cooling towards quiescence.

Spin-frequency changes attributed to disk torque effects.

Radio emission observed during minimum X-ray luminosity period.

Abstract

We show that: (i) the long-term X-ray outburst light curve of the transient AXP XTE J1810-197 can be accounted for by a fallback disk that is evolving towards quiescence through a disk instability after having been heated by a soft gamma-ray burst, (ii) the spin-frequency evolution of this source in the same period can also be explained by the disk torque acting on the magnetosphere of the neutron star, (iii) most significantly, recently observed pulsed-radio emission from this source coincides with the epoch of minimum X-ray luminosity. This is natural in terms of a fallback disk model, as the accretion power becomes so low that it is not sufficient to suppress the beamed radio emission from XTE J1810-197.