Suzaku Follow-Up Observation of the Activated Magnetar 1E 1547.0 5408

Abstract

Abstract We present broadband X-ray analyses of the magnetar 1E 1547.0$-$ 5408 observed with Suzaku on 2010 August 7, nearly one and a half years after an intense outburst in 2009 January. The 2–10 keV flux decreased to (1.06 $ \pm$ 0.01) $ \times$ 10$ ^{-11}$ erg cm$ ^{-2}$ s$ ^{-1}$ , while the hard X-ray detection was 3.5 $ \sigma$ (18–40 keV) and 2.4 $ \sigma$ (18–35 keV) significance levels, where the former includes only the 2% systematic error of the non X-ray background, and the latter further takes into account possible near-by contaminating sources, respectively. Our confirmation of both soft and hard X-ray components during the late phase of the outburst strengthened the possibility that most magnetars are composed of the two spectral components, both in burst-active and less-active states. Together with a similar decay speed between the soft and hard components, their radiation mechanisms are suggested to be tightly related to each other. The 1–40 keV broadband spectrum was successfully fitted with the same model as used in the fit just after the onset of the outburst in 2009: a surface blackbody radiation with photoelectric absorption and a hard power-law. The blackbody flux decreased to be $ \sim$ 30% of that in 2009 while keeping its temperature at $ kT$$ =$ 0.65 keV, suggesting a shrinking hotspot on the magnetar surface by a factor of 0.3. The hard power-law extended up to at least $ \sim$ 35 keV with a photon index of $ \Gamma$$ =$ 1.1 $ \pm$ 0.4, which was consistent with the 2009 value. The flux ratio, $ \xi$ , of the 1–60 keV power-law to 1–60 keV thermal component was calculated to be $ \xi$$ =$ 1.2 $ \pm$ 0.7 at the late phase of the outburst for the first time. The obtained $ \xi$ value follows the previously known negative correlation with the characteristic age, implying that the correlation holds for most of the magnetar states: no burst, onset and late phase of outbursts.