XMM-Newton discovery of 2.6 s pulsations in the soft gamma-ray repeater SGR 1627-41

TL;DR

This paper reports the discovery of 2.6-second pulsations in the soft gamma-ray repeater SGR 1627-41 using XMM-Newton, revealing its spin period and spectral characteristics after reactivation.

Contribution

First detection of the spin period of SGR 1627-41, providing insights into its magnetic and emission properties post-reactivation.

Findings

Detected 2.594578 s pulsations with high confidence

Measured pulsed fractions of 19% and 24% for fundamental and harmonic

Spectrum fitted by absorbed power law plus blackbody model

Abstract

After nearly a decade of quiescence, the soft gamma-ray repeater SGR 1627-41 reactivated on 2008 May 28 with a bursting episode followed by a slowly decaying enhancement of its persistent emission. To search for the still unknown spin period of this SGR taking advantage of its high flux state, we performed on 2008 September 27-28 a 120 ks long X-ray observation with the XMM-Newton satellite. Pulsations with P = 2.594578(6) s were detected at a higher than 6-sigma confidence level, with a double-peaked pulse profile. The pulsed fraction in the 2-12 keV range is 19% +/- 3% and 24% +/- 3% for the fundamental and the second harmonic, respectively. The observed 2-10 keV flux is 3.4E-13 erg/cm^2/s, still a factor of ~ 5 above the quiescent pre-burst-activation level, and the spectrum is well fitted by an absorbed power law plus blackbody model (photon index Gamma = 0.6, blackbody temperature kT = 0.5 keV, and absorption nH = 1.2E+23 cm^-2). We also detected a shell of diffuse soft X-ray emission which is likely associated with the young supernova remnant G337.0-0.1.