On the cooling trend of SGR 0526-66

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 per cent 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+0.031-0.024 keV and 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 9-year interval. We find a period derivative of s s-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 10151016 G for the source.