Suzaku Discovery of a Hard X-Ray Tail in the Persistent Spectra from the Magnetar 1E 1547.0$-$5408 during its 2009 Activity

Abstract

Abstract The fastest-rotating magnetar 1E 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 keV flux of the persistent emission was measured with the XIS as 5.7 $\times$ 10$^{-11} $erg cm$^{-2} $s$^{-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 $> $10 keV up to at least $\sim $110 keV, with an even higher flux of 1.3 $\times$ 10$^{-10} $erg cm$^{-2} $s$^{-1}$ in 20–100 keV. The pulsation was detected at least up to 70 keV for a period of 2.072135$ \pm $0.00005 s, with a deeper modulation than was measured in a fainter state. The phase-averaged 0.7–114 keV spectrum was reproduced by an absorbed blackbody emission with a temperature of 0.65$ \pm $0.02 keV, plus a hard power-law with a photon index of $\sim $1.5. At a distance of 9 kpc, the bolometric luminosity of the blackbody and the 2–100 keV luminosity of the hard power-law are estimated to be (6.2$ \pm $1.2) $\times$ 10$^{35} $erg s$^{-1}$ and 1.9 $\times$ 10$^{36} $erg s$^{-1}$, respectively, while the blackbody radius becomes $\sim $5 km. 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 10 keV suggests that the hard component is more enhanced than the soft X-ray component during the period of persistent activity.