1E 1547.0-5408: A radio-emitting magnetar with a rotation period of 2 seconds

The variable X-ray source 1E 1547.0-5408 was identified by Gelfand & Gaensler as a likely magnetar in G327.24-0.13, an apparent supernova remnant. No X-ray pulsations have been detected from it. Using the Parkes radio telescope, we discovered pulsations with period P = 2.069 s. Using the Australia Telescope Compact Array, we localized these to 1E 1547.0-5408. We measure P - (2.318 ± 0.005) × 10-11, which for a magnetic dipole rotating in vacuo gives a surface field strength of 2.2 × 1014 G, a characteristic age of 1.4 kyr, and a spin-down luminosity of 1.0 × 10 35 ergs s-1. Together with its X-ray characteristics, these rotational parameters of 1E 1547.0-5408 prove that it is a magnetar, only the second known to emit radio waves. The distance is ≈9 kpc, derived from the dispersion measure of 830 cm-3 pc. The pulse profile at a frequency of 1.4 GHz is extremely broad and asymmetric due to multipath propagation in the ISM, as a result of which only ≈75% of the total flux at 1.4 GHz is pulsed. At higher frequencies the profile is more symmetric and has FWHM p 0.12 P in normal radio pulsars, but in common with the other known radio-emitting magnetar, XTE J1810-197, the spectrum over 1.4-6.6 GHz is flat or rising, and we observe large, sudden changes in the pulse shape. In a contemporaneous Swift X-ray observation, 1E 1547.0-5408 was detected with record high flux, ergsf×(1-8 keV) ≈ 5 × 10-12 ergs cm-2 s-1, 16 times the historic minimum. The pulsar was undetected in archival radio observations from 1998, implying a flux <0.2 times the present level. Together with the transient behavior of XTE J1810-197, these results suggest that radio emission is triggered by X-ray outbursts of usually quiescent magnetars. © 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A.