2011A&A...531A.130B

IGRJ18410-0535 is a supergiant fast X-ray transients. This subclass of supergiant X-ray binaries typically undergoes few-hour-long outbursts reaching luminosities of 10³⁶-10³⁷ erg/s, the occurrence of which has been ascribed to the combined effect of the intense magnetic field and rotation of the compact object hosted in them and/or the presence of dense structures (``clumps'') in the wind of their supergiant companion. IGRJ18410-0535 was observed for 45ks by XMM-Newton as part of a program designed to study the quiescent emission of supergiant fast X-ray transients and clarify the origin of their peculiar X-ray variability. We carried out an in-depth spectral and timing analysis of these XMM-Newton data. IGRJ18410-0535 underwent a bright X-ray flare that started about 5ks after the beginning of the observation and lasted for ∼15ks. Thanks to the capabilities of the instruments on-board XMM-Newton, the whole event could be followed in great detail. The results of our analysis provide strong convincing evidence that the flare was produced by the accretion of matter from a massive clump onto the compact object hosted in this system. By assuming that the clump is spherical and moves at the same velocity as the homogeneous stellar wind, we estimate a mass and radius of M_cl≃1.4x10²²g and R_cl≃8x10¹¹cm. These are in qualitative agreement with values expected from theoretical calculations. We found no evidence of pulsations at ∼4.7s after investigating coherent modulations in the range 3.5ms-100s. A reanalysis of the archival ASCA and Swift data of IGRJ18410-0535, for which these pulsations were previously detected, revealed that they were likely to be due to a statistical fluctuation and an instrumental effect, respectively.