A NEUTRON STAR ULTRA-COMPACT X-RAY BINARY WITH THE SHORTEST KNOWN ORBITAL PERIOD

An ultracompact Xray binary (UCXB) candidate with potentially the shortestknown orbital period of 10.2 minutes was serendipitously discovered in theGalactic Bulge. Its only available Xray spectra from XMM, and radio/IRobservations suggest that the source may be the first direct impact NS binarywith no accretion disk or (less likely) an intermediate polar. The proposedNuSTAR+XMM observations will confirm the period for a NS spin, and identify thesource by a combination of broadband Xray spectroscopy and Fe linediagnostics. Given its short orbital period, the source may be one of the fewUCXBs detectable by the future LISA GW observatory. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]