Hubrig, S.S.HubrigSIDOLI, LaraLaraSIDOLIPostnov, K.K.PostnovSchöller, M.M.SchöllerKholtygin, A. F.A. F.KholtyginJärvinen, S. P.S. P.JärvinenSteinbrunner, P.P.Steinbrunner2020-11-122020-11-1220180035-8711http://hdl.handle.net/20.500.12386/28281A significant fraction of high-mass X-ray binaries are supergiant fast X-ray transients (SFXTs). The prime model for the physics governing their X-ray behaviour suggests that the winds of donor OB supergiants are magnetized. To investigate if magnetic fields are indeed present in the optical counterparts of such systems, we acquired low-resolution spectropolarimetric observations of the two optically brightest SFXTs, IGR J08408-4503 and IGR J11215-5952, with the ESO FORS 2 instrument during two different observing runs. No field detection at a significance level of 3σ was achieved for IGR J08408-4503. For IGR J11215-5952, we obtain 3.2σ and 3.8σ detections (⟨B<SUB>z</SUB>⟩<SUB>hydr</SUB> = -978 ± 308 G and ⟨B<SUB>z</SUB>⟩<SUB>hydr</SUB> = 416 ± 110 G) on two different nights in 2016. These results indicate that the model involving the interaction of a magnetized stellar wind with the neutron star magnetosphere can indeed be considered to characterize the behaviour of SFXTs. We detected long-term spectral variability in IGR J11215-5952, whereas for IGR J08408-4503, we find an indication of the presence of short-term variability on a time-scale of minutes. <P />STAMPAenArticle10.1093/mnrasl/slx1872-s2.0-85042194092000425491400006https://academic.oup.com/mnrasl/article-abstract/474/1/L27/4644842?redirectedFrom=fulltext2018MNRAS.474L..27HFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_6 Stars and stellar systems