Wind-fed neutron star X-ray binaries: probing stellar winds and accretion environments with compact objects

Wind-fed supergiant X-ray binaries are precious laboratories not only to study accretion under extreme gravity and magnetic field conditions, but also to probe still highly debated properties of massive star winds. These includes the so-called clumps, originated from the inherent instability of line driven winds, and larger structures. In this talk, we report on the results of monitoring campaigns that with both XMM-Newton and the Swift Neil Gehrels observatory. Data collected with the EPIC cameras allow us to carry out a detailed hardness ratio-resolved spectral analysis that can be used as an efficient way to detect spectral variations associated to the presence of clumps. Long-term observations with the XRT on-board Swift evenly sampling the X-ray emission of supergiant X-ray binaries over many different orbital cycles, are exploited to look for the presence of large scale structures in the medium surrounding the compact objects. These can be associated either to corotating interaction regions or to accretion/photoionization wakes, as well as tidal streams. All results obtained for our sample are discussed in the context of wind-fed supergiant X-ray binaries and shall ideally serve to optimally shape the next observational campaigns aimed at sources in the same classes