X-raying the brightest black widow system.

The Fermi mission unveiled a large population of MSP pulsar in the Galacticfield. A surprising, high fraction of such sources is in very compact binarysystems, the socalled (and poorly understood) Black Widows (BW) and Redbacks(RB). PSR J13113430 is one of the most interesting MSPs discovered by Fermi. Itis an extreme BW system with a number of peculiarities that make it a uniquelaboratory in order to study irradiationdriven processes ruling evolution ofMSP systems. In view of the very bright Xray counterpart, the unique,complementary capabilities of the EPIC cameras will allow to get anunprecedented view of the phenomenology of a Black widow system. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]