Swift/XRT monitoring of the candidate Supergiant Fast X-ray Transient   IGR J16418-4532
  We report on the Swift monitoring of the candidate supergiant fast X-ray transient (SFXT) IGR J16418-4532, for which both orbital and spin periods are known (~3.7d and ~1250s, respectively). Our observations, for a total of ~43ks, span over three orbital periods and represent the most intense and complete sampling of the light curve of this source with a sensitive X-ray instrument. With this unique set of observations we can address the nature of this transient. By applying the clumpy wind model for blue supergiants to the observed X-ray light curve, and assuming a circular orbit, the X-ray emission from this source can be explained in terms of the accretion from a spherically symmetric clumpy wind, composed of clumps with different masses, ranging from ~5E16 g to 1E21g. Our data suggest, based on the X-ray behaviour, that this is an intermediate SFXT. 
P. Romano, V. Mangano (1), L. Ducci (2), P. Esposito (3), P.A. Evans   (4), S. Vercellone (1), J.A. Kennea (5), D.N. Burrows...
astro-ph.HE