The long-lasting tail of a bright burst from the magnetar 1E 1547.0-5408: the effect of the dust-scattering.

We report on a bright burst, followed by an X-ray tail lasting 10 ks, detected during an XMM-Newton observation of the magnetar 1E 1547.0-5408 carried out on 2009 February 3. The burst, also observed by Swift/BAT, showed a spectral shape well described by the sum of two blackbodies with temperatures of 4 keV and 10 keV and a fluence in the 0.3-150 keV energy range of 1e-5 erg cm-2. The X-ray tail had a fluence of 4e-8 erg cm-2. Thanks to the knowledge of the distances and relative optical depths of three dust clouds between us and 1E 1547.0-5408, we carried out a spectral and temporal analysis of the tail and we found that most of the X-rays in the tail can be explained by dust scattering of the burst emission, except for the first 20-30 s after the burst. We also point out that other X-ray tails observed after strong magnetar bursts may contain a non-negligible contribution due to dust scattering.