observations of IGR J18410-0535: the ingestion of a clump by a supergiant fast X-ray transient

Context. 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-1, 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. Aims. 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. Methods. We carried out an in-depth spectral and timing analysis of these XMM-Newton data. Results. 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. 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. Conclusions. 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 Mcl ≃ 1.4 × 1022 g and Rcl ≃ 8 × 1011 cm. These are in qualitative agreement with values expected from theoretical calculations. We found no evidence of pulsations at ~4.7 s after investigating coherent modulations in the range 3.5 ms–100 s. A reanalysis of the archival ASCA and Swift data of IGR J18410-0535, for which these pulsations were previously detected, revealed that they were likely to be due to a statistical fluctuation and an instrumental effect, respectively