Suzaku discovery of a hard X-Ray tail in the persistent spectra from the magnetar IE 1547.0-5408 during its 2009 activity

Abstract

The fastest-rotating magnetar IE 1547.0-5408 was observed in broad-band X-rays with Suzaku for 33 ks on 2009 January 28-29, 7 d after the onset of its latest bursting activity. After removing burst events, the absorption- uncorrected 2-10 ke V flux of the persistent emission was measured with the XIS as 5.7 × 10-11 ergcm-2s-1, which is 1-2 orders of magnitude higher than was measured in 2006 and 2007 when the source was less active. This persistent emission was also detected significantly with the HXD in > lOke V up to at least ̃ HOke V, with an even higher flux of 1.3 x 10-10ergcm-2s-1 in 20-100ke V. The pulsation was detected at least up to 70ke V for a period of 2.072135 ± 0.00005s, with a deeper modulation than was measured in a fainter state. The phase-averaged 0.7-114keV spectrum was reproduced by an absorbed blackbody emission with a temperature of 0.65 ± 0.02 keV, plus a hard power-law with a photon index of ̃ 1.5. At a distance of 9kpc, the bolometric luminosity of the blackbody and the 2-100keV luminosity of the hard power-law are estimated to be (6.2± 1.2) x 1035ergs-1 and 1.9 x 1036ergs-1, respectively, while the blackbody radius becomes ̃ 5km. Although the source has not been detected significantly in hard X-rays during the past fainter states, a comparison of the present and past spectra at energies below lOkeV suggests that the hard component is more enhanced than the soft X-ray component during the period of persistent activity.