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) x 10(-11), which for a magnetic dipole rotating in vacuo gives a surface field strength of 2.2 x 10(14) G, a characteristic age of 1.4 kyr, and a spin-down luminosity of 1.0 x 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 approximate to 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 approximate to 75% of the total flux at 1.4 GHz is pulsed. At higher frequencies the profile is more symmetric and has. Unlike in FWHM = 0.12P 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, f(x) (1-8 keV) approximate to 5 x 10(-12) erges 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.