On the Cooling Trend of SGR 0526-66

TL;DR

This paper analyzes archival X-ray data of SGR 0526-66, revealing a 20% flux decay over nine years, stable temperature, and magnetic field estimates, providing insights into its cooling behavior and magnetic evolution.

Contribution

It provides a comprehensive spectral and timing analysis of SGR 0526-66, including flux decay, magnetic field estimation, and comparison with neutron star cooling models, which is novel for this source.

Findings

X-ray flux decayed by about 20% from 2000 to 2009.

Effective temperature remains constant within uncertainties.

Magnetic field estimated at approximately 3.7 x 10^{14} G.

Abstract

We present a systematic analysis of all archival Chandra observations of the soft-gamma repeater SGR 0526-66. Our results show that the X-ray flux of SGR 0526-66 decayed by about 20% between 2000 and 2009. We employ physically motivated X-ray spectral models and determine the effective temperature and the strength of the magnetic field at the surface as kT = 0.354_{-0.024}^{+0.031} keV and B = (3.73^{+0.16}_{-0.08})x10^{14} G, respectively. We find that the effective temperature remains constant within the statistical uncertainties and attribute the decrease in the source flux to a decrease in the emitting radius. We also perform timing analysis to measure the evolution of the spin period and the period derivative over the nine year interval. We find a period derivative of \.P = (4.0 +/- 0.5)x10^{-11} ss^{-1}, which allows us to infer the dipole magnetic field strength and compare it with the one determined spectroscopically. Finally, we compare the effective temperature of SGR 0526-66 with the expected cooling trends from magnetized neutron stars and suggest an initial magnetic field strength of 10^{15-16} G for the source.