093100

We propose contemporaneous 60 ks NuSTAR and 30 ks XMM-Newton observations of theHMGB 1FGL J1018.6-5856 during the sharp decline of the pre-periastron keV--TeVa??a??spikea??a?? of its 16.5 day orbit. With the first combinedNuSTAR+XMM-Newton observations we will monitor the evolution of the 0.7-30 keVspectral shape from the peak of the spike to after its decay to discriminatebetween the synchrotron or IC losses driving its extreme physical conditions andsearch for signatures of a NS or BH using the excellent timing resolution thanksto both NuSTAR and XMM-Newton. Thanks to their broadband capabilities largeeffective areas and superior timing resolution our observations of J1018 willreveal crucial insights on physical mechanisms driving emission in the HMGB population. [truncated! Please see actual data for full text]