X-ray and optical observations of the fast flaring HMXB A0538-66

A053866 is a Be/Xray binary (XRB) containing a 69ms pulsar that shows brightXray outbursts at periastron (up to 1E39 erg/s) associated with luminousoptical flares (up to one order of magnitude brighter than the companion starluminosity). Optical flares reaching these luminosities are not observed inother Be/XRBs. We propose three observations of A053866, each 10 ks long,during three periastron passages of the neutron star, to understand themechanism responsible for the production of fast and bright optical flares, andto search for pulsations never observed again after Einstein.s detection. Wewill use EPIC, OM, and simultaneous optical to nearinfrared observations fromour ongoing REM monitoring. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]