  A 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 FORS2 instrument during two different observing runs. No field detection at
a significance level of 3sigma was achieved for IGR J08408-4503. For IGR
J11215-5952, we obtain 3.2sigma and 3.8sigma detections (<B_z>_hydr =
-978+-308G and <B_z>_hydr = 416+-110G) 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, while for IGR J08408-4503 we find an indication of the
presence of short-term variability on a time scale of minutes.
