Quiet but still bright: XMM-Newton observations of the soft gamma-ray repeater SGR 0526-66

Abstract

SGR 0526-66 was the first soft gamma-ray repeater from which a giant flare was detected in 1979 March, suggesting the existence of magnetars, i.e. neutron stars powered by the decay of their extremely strong magnetic field. Since then, very little information has been obtained on this object, mainly because it has been burst inactive since 1983 and the study of its persistent X-ray emission has been hampered by its large distance and its location in a X-ray bright supernova remnant in the Large Magellanic Cloud. Here, we report on a comprehensive analysis of all the available XMM-Newton observations of SGR 0526-66. In particular, thanks to a deep observation taken in 2007, we measured its pulsation period (P = 8.0544 ± 0.0002 s) 6 years after its latest detection by Chandra. This allowed us to detect for the first time a significant reduction of its spin-down rate. From a comparison with two shorter XMM-Newton observations performed in 2000 and 2001, we found no significant changes in the spectrum, which is well modelled by an absorbed power law with NH = 4.6+0.7-0.5 × 1021 cm-2 and Γ = 3.27+0.07-0.04. The high luminosity (~4 × 1035 erg s-1, in the 1-10 keV energy band) still observed ~25 years after the latest detection of bursting activity places SGR 0526-66 in the group of bright and persistent magnetar candidates. © 2009 The Authors. Journal compilation © 2009 RAS.