The Supergiant Fast X-ray Transients taken to new extremes

The Supergiant Fast X-ray Transients (SFXTs) are X-ray binaries showing a very variable X-ray flux. However, they reach also other kinds of extreme behaviors: we discuss here recent results about the least and the most absorbed SFXTs. IGR J08408-4503 is the least absorbed SFXT. A new XMM-Newton observation caught it in a faint state and thanks to the very low absorption towards the source, the X-ray spectrum could be deconvolved to three spectral components: two collisionally ionized plasmas plus a steep power-law model dominating above 2 keV. We interpreted the two-temperature plasma as the intrinsic X-ray stellar wind emission from the donor star (LM Vel), while the power-law as residual accretion onto the compact object. The emission contributed by the power-law component only (5x10^31 erg/s) is the lowest X-ray luminosity detected from the compact object in a SFXT. The candidate SFXT AX J1714.1-3912 is the most absorbed source. Its long-term X-ray emission shows a huge variability in its absorbing column density: here we report on the discovery of a very high obscuration (10^24 cm-2) serendipitously observed by XMM-Newton together with a 6.4 keV iron line. These properties make it one of the most absorbed sources in our Galaxy, resembling the so-called "highly obscured sources" discovered by INTEGRAL