Spin - down rate and inferred dipole magnetic field of the soft gamma - ray repeater SGR 1627 – 41

Using Chandra data taken on 2008 June, we detected pulsations at 2.594 39(4) s in the soft gamma-ray repeater SGR 1627–41. This is the second measurement of the source spin period and allows us to derive for the first time a long-term spin-down rate of (1.9 ± 0.4) × 10 s s. From this value we infer for SGR 1627–41 a characteristic age of ∼2.2 kyr, a spin-down luminosity of ∼4 × 10 erg s (one of the highest among sources of the same class), and a surface dipole magnetic field strength of ∼2×10 G. These properties confirm the magnetar nature of SGR 1627–41; however, they should be considered with caution since they were derived on the basis of a period derivative measurement made using two epochs only and magnetar spin-down rates are generally highly variable. The pulse profile, double-peaked and with a pulsed fraction of (13 ± 2)% in the 2–10 keV range, closely resembles that observed by XMM-Newton in 2008 September. Having for the first time a timing model for this SGR, we also searched for a pulsed signal in archival radio data collected with the Parkes radio telescope nine months after the previous X-ray outburst. No evidence for radio pulsations was found, down to a luminosity level ∼10–20 times fainter (for a 10% duty cycle and a distance of 11 kpc) than the peak luminosity shown by the known radio magnetars.