XMM-Newton observations of IGRJ18410-0535: The ingestion of a clump by a supergiant fast X-ray transient

IGR J18410-0535 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. IGR J18410-0535 was observed for 45 ks 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. IGR J18410-0535 underwent a bright X-ray flare that started about 5 ks after the beginning of the observation and lasted for ~15 ks. 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 ~1.4×10²² g and 8×10¹¹ cm.